1,3-dipolar cycloadditions, 98 the chemistry of thiocarbonyl s-sulfides

7-erra/wfmn. Vol. 53. No. 3, 939.960, 1997 P,I

CopyrIght 0 1996 Elsewer Science Ltd Printed in Great Britain. All rights reserved

PII: SOO40-4020(96)01068-X 0040.4020/97 $I 7.00 + O.Oil

1,3-Dipolar Cycloadditions, 98 ’

The Chemistry of Thiocarbonyl S-Sulfides

Rolf Huisgen * and Jochen Rapp Institut fiir Organische Chemie der Universit$t Miinchen

Karlstr. 23, D-80333 Miinchen, Germany

Abstmct: 3,3,&S-Tetraaryl-1,2,4-trithiolanes (1) equilibrate in solution with diary1 thioketones 2 and their S-sulfides 7 (thiosulfines). Activated acetylenes (DMAD, dicyanoacetylene, cyclooctyne) as di- polarophiles capture 7 furnishing 1,2-dithioles. A sulfur transfer from 2,2-diphenylthiirane to thiones gives rise to thione S-sulfides 7 which quickly form 1,2,4-trithiolanes with a second molecule of thione. According to kinetic measurements, the desulfurizations of diphenylthiirane by thiones are slower than those by P(I11) compounds and follow the second order. 1,2,4-Trithiolanes and thiones undergo metathesis reactions via cycloreversion-cydoaddition. Thione S-sulfides are not isolable, but decompose to thiones and elementary sulfur by fast sulfur transfer reactions. The MS of the 1,2- dithiolanes and 1,2,4_trithiolanes reveal the importance of distonic radical ions. CopyrIght 0 1996 Elsevier Science Ltd

Introduction

A ghostly existence of the so-called thiosulfines - usually formulated as RR’C = S = S - began in

1921.2 Claims were countered by refutations; often the thiosulfines turned out to be the formal dimers.

1,2,4,5_tetrathianes. Sometimes thiosulfines were just assumed to satisfy stoichiometric equations. The

first 60 years of the history of thiosulfines were well reviewed.3T4 In 1986 Senning et al. published

“evidence for the intermediacy of dithiiranes and thiosulfines” which was based on the ring closure of

thiosulfines to dithiiranes, followed by rearrangement to dithiocarboxylic esters and subsequent

conversions.5 This rearrangement has not yet been observed since thiosulfines became accessible.

In 1987 we published a communication on thione S-sulfides as “the first unequivocal evidence for

their existence”.6 Since no opposition was voiced, we are giving here the experimental account of two

pathways leading to this new class of 1,3-dipoles; on the basis of their cycloadditions, we prefer the

zwitterionic octet formula to the one with cumulated double bonds. Further papers on the intermediacy

of thione S-sulfides appeared recently; they will be discussed in the light of our report.

Aromatic Thione S-SulJides by P,3-Dipolar Cycloreversion

In 1928 Staudinger and Freudenberger studied the autoxidation of crystalline thiobenzophenone

(2a), when stored for 6 d at room temp. under dry oxygen;7 3,3,5,5-tetraphenyl-1,2,4-trithiolane (la) was

isolated in up to 52% yield, based on the sulfur content of 2a. Only small amounts of la resulted from

939

940 R. HUISCEN and .I. RAPP

autoxidation in solurion. The colorless crystals of la turned blue at the melting point, the color of Za; af-

ter 5 min at 130 “C the decomposition was complete affording 81% of 2a and elementary sulfur.7 Still in

1928, Schonberg’s laboratory likewise reported la as product of the autoxidation of 2a.* The alternative

structure 3 for the compound C2eH2,,S3 was excluded by hydrogenolysis with Raney nickel furnishing

diphenylmethane.9

(C,H,),&S 130°C Cd-L

S+H) __+ * ‘c=s

6 52 Q-f:

+ ; s,

la 2a

A more convenient access to la consists of reacting 2a with tetrachloro-o-quinone (4) in ether (3

weeks at 2 “C), as described by Schonberg and K&rig. lo The yield of 54% was based on the reaction of 4

with 3 molecules of 2a; 74% of the benzodioxole 5 was isolated under slightly different conditions.1°

The reaction looks somewhat mysterious; a possible mechanism will be proposed later. By keeping the

molar ratio 1:3 for 4/2a, we obtained 73% of la. A second method, described below, supplied us with

higher yields of la and other 1,2,4_trithiolanes.

The formation of the blue 2a from the colorless la does not require 130 “C. It was noticed by the

discoverers 7,8 that solutions of la in ether or benzene turned blue on longer storage at room tempera-

ture. What are the energetics of a dissociation of la into 2a and sulfur ?

A thermal fragmentation of la into 2 molecules of 2a and a sulfur atom is allowed to be concer-

ted by orbital control. However, the singlet sulfur atom (tD2) is a high-energy species; it has a AH, of

93 kcal mol-‘, based on S,. *1,12 Furthermore, the fragmentation of la would be burdened by the con-

version of u-bonds, C-S and S-S, into n-bonds C= S.

The simplest way of avoiding the occurrence of S(‘D,) would be the cleavage of la into thio-

benzophenone S-sulfide (7a) and 2a, a straightforward 1,3-dipolar cycloreversion, symmetry-allowed as

a concerted process. The S-sulfide 7a, alias diphenylthiosulfine, belongs to the class of thiocarbonyl be-

taines.13 Reversible 1,3-dipolar cycloadditions to thiones have been reported for thiocarbonyl y1ides,14

thiocarbonyl imines,t5 and thiocarbonyl oxides (sulfines).t6 Like thiocarbonyl ylides, the sulfide 7a can-

not be isolated. However, both products of the cycloreversion are interceptible.

Thione S-Sul~es and Activated Acetylenes

When the solution of la and 2.2 equiv. of dimethyl acetylenedicarboxylate (DMAD) in chloroform

was refluxed, the blue color of 2a appeared after 10 min. The color changed to light-green during the

subsequent 24 h of refluxing. The separation of the cycloadducts 6a and 8a was achieved by thick-layer

chromatography. The yellow crystalline dimethyl 3,3-diphenyl-3H-1,2-dithiole-4J-dicarboxylate (6a)

I J-Dip&r cycloadditions-XCVIII 941

was isolated in 59% yield and the benzothiopyran derivative 8a in 94% yield. In an experiment without

solvent (4 equiv. of DMAD, 4 h 60 “C), quantitative ‘H NMR analysis with weight standard indicated

83% of 6a and 68% of 8a.

Ar 4>r _--,

2

1

S Ar, 3 ‘S

k

DMAD

4_5

_

CH,O,C CO,CH,

6

Ar,

Ar t

Ar, ,S, C’ ’ s

Ar

7

a Ar = C,H, b Ar = C,H,CI-p

+ Ar,C=S

2

+ DMAD

R CO&H,

8a R=H

8b R=CI

Di-p-chlorothiobenzophenone S-sulfide (7b) served as a second model. Analogously generated

from trithiolane lb in refluxing chloroform, it was captured by DMAD to give the dithiole 6b in 68%

yield. The second product of cycloreversion, 2b, combined with DMAD to 72% of 8b.

The formation of the lH-2-benzothiopyrans 8 is a Diels-Alder reaction followed by 1.3 proto-

tropy. The prototype, 2a + DMAD, has been described by Gotthardt and Nieberl:17 we will deal with

new aspects of this (4 + 21 cycloaddition in the subsequent paper.18

Besides the elemental analyses, the spectra were in accordance with the dithiole structures 6.

The light absorptions at 1 max 392 nm for 6a and 391 nm for 6b are responsible for the yellow color.

Due to symmetry, the ‘H and 13C NMR signals of the two phenyl or 4-chlorophenyl groups, respecti-

vely, were identical. The olefinic C-4 and C-S appear at 6c 138-142, whereas the benzylic C-3 occurs at

79.1 and 80.2 for 6a and 6b.

GW2C\H 2 3

,CH-C\H, WJ2~,

CH,O,C CO,CH, /c-y2

CH,O,C CO,H

9 10

Hydrogenolytic removal of sulfur from the dithiole 6a by Raney nickel provided dimethyl 2-

benzhydrylsuccinate (9) in 75% yield. The protons of 3-H, show diastereotopicity in the ‘H NMR

spectrum, and two sets of 13C shifts point to diastereotopic phenyl groups. The benzhydryl cation is the

base peak in the MS of 9. The independent synthesis of 9 consisted of Stobbe condensation of benzo-

phenone with dimethyl succinate, followed by catalytic hydrogenation of the half-ester 10 and esterifica-

tion by diazomethane.

942 R. HUISGEN and J. RAPP

Dicyunoacetylene was likewise active in scavenging the dissociation products of la,b. In the deep

yellow dithiole lla, isolated in 76% yield, the long-wave light absorption has shifted to 412 mn. For the

unstable dichloro compound llb no satisfactory analyses were obtained. In contrast to simple alkylated

acetylenes, the angle-strained cyclooctyne was capable of intercepting the thione S-sulfides 7 and the

thiones 2. When la was heated with 4 equiv of cyclooctyne to 60 “C, the colorless solution turned blue,

then green, and within 4 h to yellow. The yellow crystals of 12a (66% yield) showed in chloroform with

A max 373 mn a hypsochromic effect, compared with 6a and lla. The di-p-chloro derivative 12b (55%)

remained oily, but gave correct analyses.

11 a Ar=C,H, 12

b Ar = C,H,CI-p

13 a R=H 14

b R=CI

The literature on 1,2-dithioles is mainly concentrated on 1,2-dithiolium cations and l,Zdithiole-

3-thiones. The cycloadditions of thiocarbonyl S-sulfides supplement existing syntheses.” The type of

1,2-dithiole occurring here has not been described as far as we know.

Mass Spectra of I,.&Ditizioles

In the MS of the l,Zdithioles, the molecular peak reaches the 20% level. Mf is probably not the

cyclic radical cation, but rather the open-chain, energetically favored distonic species 15 in which charge

and spin density have different centers.20p21 Benzylic C-S cleavage gives rise to 15 which profits from the

resonance of the benzhydryl cation. Another type of benzylic splitting, the loss of Ar’, produces the

aromatic dithiolium ion 19 (peak intensities 7-20%).

S’ Ar,: ‘S

‘CZC’

d k

Ar,; S’

‘CZC’

R’ k

Ar,;

‘C=C.

R’ k

+. Ar,C=C=CR,

15 [M+] 16 [M+-S] 17 [M-2S] 18

a Ar= C,H, b Ar = C,H,CI-p R = CO&H,, CN ; R, = -(CH,),-

19 [M+- Ar] 20 X = H, Cl 21 [ M+- 2s - CH,OH ] 22 [ M - 2s - E ]

I ,3-Dipolar cycloadditions-XCVIII 943

Most of the further fragments are derived from the type 15. The peaks [Mt.- 2S] (17 or 18) are

strong and in two cases the base peaks. With low intensity (l-S%) the [M+‘- S] peak 16 appears. The

major pathway, however, is the loss of S,. A signal at m/z 64 is tentatively assigned to S2+; too much

“trash” thwarts the search for isotope peaks in the low mass region. We made ample use of the intensi-

ties of 13C, 34S and 37C1 satellites - they turned out to be excellent probes for molecular formulae of

fragments, especially the larger ones. The cations Ar-C=S+ are minor, but regular companions; 19 may

be the logical precursor.

The radical cations of the 1,2-dithioles do not undergo cycloreversion to 7+’ and the acetylenic

dipolarophile. The expected signals of Za+’ and 2b+’ are missing, and those for the fluorenyl cation 20

and its dichloro derivative - base peaks in the MS of thiones 2a,b - are likewise unimportant. Obviously,

the ease of benzylic cleavage suppresses other fragmentation pathways.

In the MS of the dicarboxylic esters 6a,b the elimination of methanol from 17 generates major

peaks: 78% for 6a and 100% for 6b. A ring closure with an aryl group is likely, but the indenoketene

formula 21 is speculative. The loss of an ester group from 17/H? is another follow-up, suggesting the ca-

tion 22 (95% for 6a, 15% for 6b).

1,2,4-Trithiolunes and Ekiones: Metathesis

The mobile equilibrium of trithiolanes 1 with 7 t 2 indicates that thione S-sulfides 7 easily com-

bine with thiones. When la or lb was refluxed with 1.4 equiv of adamantanethione (23) in chloroform,

the adamantane-Spiro-1,2,4-trithiolanes 24a and 24b were isolated in 81% and 83% yield. The formula

1 23 24 2

a Ar= C,H, b Ar = C,H,CI-p

scheme above neglects the intermediacy of thione S-sulfide 7, but emphasizes the thermodynamic que-

stion: What drives the metathetical equilibrium of trithiolane t thione from left to right despite the ste-

ric hindrance of 23 ? It is the conjugation energy of the aromatic thiones 2a,b which is set free.

24a

r_* (C,H,),C=S +

26


The dissociation of 1 into 7 + 2 may still be small at 60 “C, but that of 24a,b is negligible; the

blue color of 2a,b was not visible in boiling chloroform. However, at the melting point (131 “C for 24a

and 124 “C for 24b) the blue color slowly appeared. Heating of 24a with an excess of 23 to 130 “C produ-

ced a deep-blue melt from which 56% of the dispiro-trithiolane 26 was isolated. Of the two conceivable

directions of 1,3-dipolar cycloreversion, the one giving rise to the conjugated thione 2a and thione S-sul-

fide 25 is realized.

The analogous cycloaddition of 7a to the C=S bond of 2,2,4,4-tetramethyl-3-thioxocyclobuta-

none was recently reported from this laboratory in another context.’ Thiones are superdipolarophiles -

with respect to the rate constants, not the free energy changes. Thiobenzophenone S-sulfide (7a) pro-

bably combines with 2a much faster than with the activated acetylenes; however, thermodynamics gives

the dissociation of la a chance, Le., an equilibrium of la with 7a + 2a is established. The interplay of

rates and equilibria is similar to that in nitrone cycloadditions: thiones react faster than CC double and

triple bonds, but equilibria are achieved in the case of thiones.22

Mass Spectra of 1,2,4-Trithiolanes

In the MS of 24a strong peaks for the radical cations 2a+’ (69%) and 23+’ (100%) leave no

doubt that cycloreversions constitute the major fragmentation whereas the M+ peak is small. The

assignment of m/z 230 (13%) to C,,H,uS2 + is confirmed by the intensity of the 34S peak; thus, the dis-

tonic radical cation 7at ’ survives to some extent, before it loses sulfur. The peak m/z 198 could be 2a+

or 25+‘; the 34S intensity clearly favors 2a” , but can not exclude a minor amount of 25+’ . The MS of

24b allows the distinction: Both 7bt’ (6%) and 25+. (18%) occur, although the major fragments are

2bt’ (79%) and 23+’ (100%).

+ +

Ar,C Gs\S’ + AdC=S

7+- \

23

Ar,C .6 - +’ /

‘S + AdC=S

7 23+’ 24+’ 2 +. 25

a Ar = C,H, Ad = b Ar = C,H,CI-p

Thus, in the two cycloreversions of 24+’ the positive charge may reside on each of the splitting

products. Possibly, formula 24+‘has to be replaced by an equilibrium mixture of ring-opened distonic

radical cations. Finally, in the MS of the bis-Spiro-adamantane 26, the species 25+’ is even the base

peak, and 23’. is populated to the extent of 32%.

A third fragmentation of 24 + ’ consists of S, elimination and formation of the distonic radical ca-

tion 27 which is the formal ionization product of a thiocarbonyl ylide. The intensities of the 34S, 35C1,

I .3-Dipolar cycloadditions-XCVIII 945

and 13C isotope peaks secured [M’ - 2S]: 16% of 27a from 24a’ and 7% of 27b from 24b+ as well as

9% of 28 in the MS of 26. The ion radicals 27 and 28 may well be in equilibrium with the thiirane radi-

cal ion 29 which, in turn, could lose sulfur leading to 30. Although [M+ - 3S] was not found in the MS of

24 and 26, the radical ion 30a (22%) occurred in the MS of trithiolane lb. Correspondingly, the radical

cation of 9,9’-bifluorenylidene (30b, 68%) showed up in the MS of trithiolane 43 (vide infrcz).

+ +

/Q&Ad Ad 6’ %Ad R&L a R = p-Cl&H,

2 2 R,Cf=‘CR,

27 28 29 30

The olefinic carbon atoms of 30 were not linked in the 1,2,4_trithiolanes. The conclusion that the

MS is unsuitable for the differentiation of 1,2,4-trithiolanes and their 1,2,3 isomers would be premature.

The high peak intensities of R,C=S+’ in the MS of lb (87%) and 43 (100%) would be incompatible

with a 1,2,3-trithiolane structure.

As reported long ago, 2a+ ’ breaks down into fluorenyl’ + HS’ , and a reasonable sequence of

steps was proposed.23 It is not astounding, that fluorenyl appeared in the MS of 24a (98% of 20. X =

H) and its dichloro derivative 24b (40% of 20, X = Cl).

Thermolysis of Thiobenzophenone S-Sulfide (7a)

Whereas the system 1,4,2-oxathiazolidine 7 nitrone + thione is kinetically stable,22 the cyclo-

reversion equilibrium of trithiolane la is continuously disturbed by the disappearance of the 1,3-dipole

7a. How does the seemingly simple splitting of thiobenzophenone S-sulfide (7a) into 2a and elementary

sulfur come about ?

Numerous sulfur extrusions are known in organic chemistry. Usually, authors contented themsel-

ves with writing -S under the reaction arrow; the more scrupulous used -(S). The thermochemical di-

lemma in assuming the intermediacy of the sulfur atom has been considered above. The high heat of

formation of singlet S(‘D2) should drive up the activation energy of such processes. The splitting of S-

sulfide 7a into 2a + l/8 S, , however, takes place in moderately warm solutions of la and cannot have a

high activation energy.

+

* (Q--W As- _--, (CBHJ2C=S + (C,H,)2C5S~S-S-

7a 2a 31

8 &j-LJ2C=S +

2a

- /pT .._ S S

32 6 6 ‘s-s’

6 further S transfers from 7a


Transfers of formal sulfur atoms between anionic sulfur chains are fast, according to our experi-

ence even fast on the NMR time scale.24 A disproportionation equilibrium of two molecules of S-sul-

fide 7a with 2a and thione S-dithiolate 31 is conceivable. With the splitting of 31 into 2a and S, (AH,

’ 30.8 kcal mol ), 25 the energy balance would become more advantageous. However, further sulfur

transfer equilibria could rapidly build up sulfur chains which roll up and shed cyclooctasulfur, the

favored species in such equilibria. The free energy level will be lowered in the net conversion of 8

molecules of thione S-sulfide into 8 molecules of thione plus S,. Other ring sizes of elementary sulfur

may occur as well.

Senning et al. conjectured that thiosulfines would undergo electrocyclic ring closure to dithiira-

nes which, in turn, would rearrange to dithiocarboxylic esters5 The sequence is formulated below for

7a, and phenyl dithiobenzoate (34) should be formed via 33: usually phenyl ranks high in migratory

aptitude.

We tested the analytical limits for 34 - the red crystalline solid was independently prepared - in

an excess of thiobenzophenone. In artificial mixtures, the strong IR bands at 740 and 858 cm*’ allowed

to recognize 1% of 34 in 2a; thione 2a and the solvent CS, have “windows” at these wave numbers.

7a

Trithiolane la (0.5 M) was refluxed in chloroform for 16 h; in a second experiment, the melt of

la was heated to 130 “C for 1 h. The subsequent distillation (120-140 “C/1O-3 torr) furnished 2a in yields

of 75% and 78%, respectively; the IR spectrum did not reveal 34, i.e., the amount in which it arose, if

any, must have been less than 1%.

The assumption of an equilibrium of thione S-sulfides with dithiiranes ’ may well be correct.

Only the open-chain form, 7a, would profit from phenyl conjugation. However, there is no doubt that 7a

is the species responsible for the 1,3-dipolar cycloadditions described above. It may be recalled that the

1,3-cycloadditions of aziridines are preceded by a rate-determining unimolecular conrotatory ring ope-

ning to give azomethine ylides.Xy27 The barrier heights for the electrocyclic ring openings of aziridines

and oxiranes are substantial and put into question the mobility of equilibria of thione S-sulfides with

dithiiranes.

35 36

In 1994, Ishii, Nakayama et af. reported on 35, the first isolated dithiirane, substituted by phenyl

and rert-alkyLw Its thermal conversion to 36 reveals the ring opening to a thione S-sulfide with subse-


quent intramolecular trapping. An example for the predicted rearrangement of a thione S-sulfide or

dithiirane to a dithiocarboxylic ester has still to be uncovered.

The mechanism outlined above for the conversion 7a + 2a + l/8 S, may well be applied to the

sulfur extrusions of other 1,3-dipoles with terminal thiolate function. Benzonitrile N-sulfide, C,H,-

C=N+ S, is intercepted by cycloadditions to nitriles 29 and activated acetylenes;30 in the absence of di-

polarophiles, benzonitrile and elementary sulfur are found. Dinitrogen sulfide, N=N t S, is stable at

77K and decomposes on warming.3’ The intermediacy of thiosulfoxides, RR’SLS, in the reaction of

sulfoxides with P,S,o or B,S, is highly probable, but the fast sulfur loss thwarts direct evidence.32

Conversion of llziones to Thione S-Sulfides

Treatment of thiones with peracids furnishes thione S-oxides;33 formally an oxygen atom is atta-

ched. Which reagent may be capable of transferring a formal sulfur atom to the double-bonded sulfur

of thiones ?

Phosphanes and phosphites are the reagents of choice for the conversion of thiiranes into olefins.

It was argued in our laboratory in another context that thiones might also be capable of desulfurizing

thiiranes. In an experiment of 1981, 3-methyl-2,2_diphenylthiirane (37) was treated with 2.2 equiv of 2a

in ether at room temp. for 24 d; 84% of la precipitated and NMR analysis indicated 90% of l,l-diphe-

nylpropene (40) in the mother liquor.6y34

(C,H,),C=S + (C,H,),&

S + (C6H,)&=CH-R

2a 37 R = CH, 39 40 R =CH, 38 R=H I 41 R=H

la 7a

Thus, the sulfur of the thiirane became attached to the thione sulfur giving rise to the thione S-

sulfide 7a. The zwitterion 39 is the plausible intermediate which undergoes cheletropic elimination. With

the concluding cycloaddition to the superdipolarophile 2a, we return to the equilibrium with the tetra-

phenyl-1,2,4-trithiolane (la) discussed above.

The equilibrium concentration of the unstable 7a is minimized when the reaction of 2,2-diphe-

nylthiirane (38) with 2.5 equiv of 2a was carried out in pentane at 20 “C. After 12 h the colorless, scar-

cely soluble trithiolane la began to crystallize, and 92% each of 2a and 1,1-diphenylethylene (41) was

analyzed after 14 d. By the same procedure, the tetrachloro derivative lb was obtained in 67% yield af-

ter 10 d, and thiofluorenone (42) was converted to the bis-Spiro-trithiolane 43. The sulfurization of

adamantanethione (23) by 38 yielded the trithiolane-bis-spiroadamantane 26 via the thione S-sulfide 25.

1,3-Dipolar cycloadditions-XCVIII 949

Figure 1. Kinetics of desulfurization of

thiirane 38 (A) by thiones 2a,b (B) in

CDCl, at 34.0 “C

Time (hours)

4.4’-Dichlorothiobenzophenone (2b) was by a factor of 1.6 faster than 2a in the sulfur transfer

from 38, whereas adamantanethione (23) was 16 times slower. Triphenylphosphane exceeded 2a 48-fold

in the rate of desulfurization (Table 1).

Table 1. Rates of Desulfurization of 2,ZDiphenylthiirane (38, A) by Various

Reagents (B) in CDCI, at 34.0 “C

Reagent B,

(MI

W&Q 0.250

2a 0.762

2b 0.787

23 (CsDs) 1.558

47 0.743

48 0.775

A0 (M)

0.250

0.305

0.314

0.639

0.305

0.304

Evaluation to Correl. ldkz

o/o conversion coeff. r (M-kl)

78 0.9987 139

88 9982 2.9

93 9976 4.6

73 9960 0.18

84 9856 0.74

74 9951 0.62

Kinetic findings never prove a pathway, but are at best in accordance with a proposed one. Rigo-

rously excluded are mechanisms which require other rate equations, e.g., a complex of two molecules of

thione reacting with the thiirane. A zwitterion 46 (or diradical) is conceivable on the pathway of thione

dimerization furnishing 1,3-dithietanes. If we hold thiirane 38 responsible for the insertion of the third

sulfur 1,4 into 46, this would provide the trithiolane la on a pathway which avoids the intermediacy of

the thione S-sulfide. A preceding equilibrium with 46 would require a dependence on the square of the

thione concentration, incompatible with the kinetic results. The transfer of a formal S atom from thi-

irane to the thione finds a convincing analogy in the role of a phosphane as sulfur acceptor. Further-

more, the evidence for an equilibrium of the trithiolane with thione S-sulfide + thione (see earlier sec-

tion) requires the cycloaddition step assumed here as a logical consequence.

The kinetic behavior of thiofenchone (47) and selenofenchone (48) vs. thiirane 38 deviated mar-

kedly from that of 2 and 23. The measured concentrations fit the first order for 38, but 47 and 48 were


not consumed; they act as catalysts. We assume that the sulfur transfer proceeds normally. Due to steric

hindrance, the S-sulfides 49 and 50 are no longer capable of undergoing 1,3cycloadditions to the se-

cond thione or selone molecule. They decompose by disproportionation reactions of the type outlined

above for 7a with 31 and 32 as intermediates. Thus, 47 and 48 catalyze the conversion of thiirane 38

into l,l-diphenylethylene and elementary sulfur. We regard the reaction course here as a model for al-

legedly spontaneous sulfur extrusions from thiiranes which in our opinion are catalyzed elimina- tions 24,39,4

” 47 x=s 49 51

48 X = Se 50

An example for a thiirane desulfurization catalyzed by the thiourea 51 was described by Janulis

and Arduengo III in 1983 and likewise interpreted with an intermediate thione S-sulfide.41

Related Conversions of Thiones to Thione S-Sulfides

Tetracyanoethylene oxide is capable of transferring C(CN), to nucleophiles. Linn and Ciganek

studied the reaction with 2a and isolated la (51%) and 2,2-diphenylethylene-l,l-dicarbonitrile (48%).42

The authors suggested that thiirane 53 was involved; we regard thiobenzophenone dicyanomethylide

(52) as a reasonable precursor. It is known that tetrasubstituted thiocarbonyl ylides no longer undergo

cycloadditions, but prefer electrocyclization to give thiiranes.43 53 would be the sulfur donor for the

pathway to la.

5 $y GH5)2

Cl O 53 X = C(CN), 54 X = N-Ar

For experiments with thione S-sulfides on a preparative scale, phenylated thiiranes like 37 or 38

may not be the most convenient equivalent of the sulfur atom. Which other reagents have been found

suitable ?

As mentioned at the beginning, Schijnberg and Konig treated 2a with tetrachloro-o-benzoqui-

none (4) and obtained trithiolane la and benzodioxole 5. lo The thioxiranium zwitterion 55, formed in

two steps, is a conceivable intermediate; 55 should be highly prone to transferring its sulfur onto 2a.

Recently we discussed a possible role of Spiro-oxathiirane 56 as a sulfur transfer agent in the re-

action of thiobenzophenone S-oxide with 2,2,4,4-tetramethyl-3-thioxocyclobutanone.’ Mloston and

1 $Dipolar cycloadditions-XCVIII 951

Heimgartner made the thiaziridine 54, assumed intermediate in the reaction of aryl azides with 2a, re-

sponsible for the sulfurization of 2a and trithiolane formation.44

In 1967 Elam and Davis converted tetramethylcyclobutane-1,3-dione into the dithione by treat-

ment with P,S,, in pyridine; a minor amount of a 1,2,4-trithiolane was isolated.45 Nakayama et aI.&

treated the dithione 57 with Lawesson’s reagent 47 (LR) in refluxing xylene; the isolated trithiolane 58

(28%) resulted from the intramolecular cycloaddition of a thione S-sulfide. Saito et al. converted ketone

59 with LR to the dithiepin 60 (15%) and conjectured a [5+2] cycloaddition of an intermediate a, B-

unsaturated thiocarbonyl S-sulfide to the C = C double bond.48 In such processes, P(V) sulfides must be

reduced to P(III) compounds. Oddly, the yield of 60 was not increased by the addition of S, to the LR.

57 58 59 60

Staudinger and Meyer used elementary sulfur to convert phosphorane 61 into 2a.49 In 1993

Okuma et al. treated 61 with 7 equiv of S (Ss) in the presence of maleic anhydride in boiling xylene;

74% of 62 left no doubt that 7a was intercepted.jO When 2a instead of 61 was applied, the yield of

dithiolane 62 shrunk to 15%. Somewhat mysterious is an earlier report that an additional source of sul-

fur is not required; 18% of the same adduct 62 resulted just on refluxing of 2a with maleic anhydride in

xylene.51

Wai and Sammes reported the formation of the dispiro-1,2,4-trithiolane 26 (82%) from 23 and

elementary sulfur in refluxing xylene.52 The intermediacy of the thione S-sulfide 25 appears straight-

forward, but the mechanism responsible for it is not. Is the open-chain S, diradical the transfer rea-

gent ? Or is nucleophilic or electrophilic catalysis involved as in the “spontaneous” desulfurizations of

thiiranes ? We suspected the polythiolate anion, R-S,-, formed from S, + nucleophilic catalysts, to be

the reactive species. However, S, plus a trace of sodium thiophenoxide interacts differently with thio-

nes, as will be described elsewhere from our laboratory.

C6% ‘C q P(C,H,),

C,H:

(“‘~& 6 @

CH, 61

CH, 62 63 64

According to Saito, Motoki et al., the thioketone 63 was converted to the 1,Zdithiolane 64 in

56% yield by S, in refluxing xylene;53 an intramolecular [3 +2] cycloaddition of thione S-sulfide was as-

sumed. Somewhat irritating is the observation that 44% of 64 were formed by refluxing 63, without any

9.52 R. HUISCEN and J. FCAPP

S,. Obviously, the thioketone itself can be converted to a sulfur donor capable of generating the thione

S-sulfide in an unknown pathway. We conjecture that a trace of H,S t 0, might be a candidate for the

catalyst system.

The involvement of thione S-sulfides in trithiolane formation is even less unequivocal in one-pot

procedures in which ketones are treated with amines, H,S and elementary sulfur. According to Asinger

et uZ.,~~ tetraethyl-1,2,4_trithiolane is formed in 92% yield when diethylketone is treated with bu-

tylamine, H,S and “flowers of sulfur” for 12 h at 2.5 “C; a little defined sequence of addition, elimination,

and redox reactions was assumed. Similarly, the reaction of cyclohexanethione with S, and triethyl-

amine in ethanol at room temp. furnished the corresponding dispiro-1,2,4-trithiolane in 68% yield.55

When a solution of 2a in benzene was stirred with aqueous methylamine (20 “C, 30 s), 14% of

trithiolane la was isolated besides some benzophenone, according to Campbell and Evgenios.56a Is 0,

as oxidant required ? The same authors converted 2a by chloramine T in ethanol to 90% of la, based

on the sulfur content; the interpretation of 1973 56b may have to be changed. Thiones and chloramine T

furnish thione S-imides, as found in the meantime.57 A cascade of cycloaddition and cycloreversion re-

actions could give rise to la.

More work is required to clarify the mechanistic pathways. Certainly the 1,2,4_trithiolane ring

stands out through its formation tendency.

65 66 67 68

This paper focusses on the conversion of thiones to their S-sulfides. Briefly mentioned may be

another access to thiocarbonyl S-sulfides. Okazaki et al. treated ketone hydrazones with S,Cl,/triethyl-

amine and obtained thioketones;58 the reaction pathway via 65 and 66 to thione S-sulfides was an

intelligent guess, and the authors discussed other mechanisms, too. The hypothesis became viable when

Machiguchi et al. reacted tropone hydrazone with that reagent at -78 ‘C; the successful isolation of the

DMAD adduct 68 (23%) established the intermediacy of tropothione S-sulfide (67).59

EXPERIMENTAL

Geneml. IR spectra were recorded with a Bruker FT model IFS 4.5. UV/Vis spectrophotometer:

Perkin-Elmer Lambda 3; spectra in CHCl,, 3L max in nm (log E). ‘H NMR spectra were obtained with

Bruker WP8OCW (80 MHz), and 13C NMR spectra with Bruker WPSODS (20 MHz). All NMR spectra

were taken in CDCl, with TMS as internal standard; the CDCl, was kept acid-free by storing over dry

potassium carbonate. For quantitative ‘H NMR analyses, a weighed standard was added after the end

of the reaction; 1,1,2,2-tetrachloroethane (s-TC, b 5.92) and its 1,1,1,2 isomer (as-TC, 6 4.28) served

as standards . The amount of standard was so chosen that the integral of the singlet was comparable to


those of the signals to be analyzed. - Mass spectra: AEI Manchester MS 902 and Finnigan Mat 90; the

electron impact spectra were run with 70 eV. The intensities of isotope peaks (13C, 34S, 37Cl) were

compared with those calculated on the basis of the main isotopic composition; results are given in the

form, e.g., 13C calcd/found. - Preparative layer chromatography (PLC): 2 mm silica gel 60 PF (Merck)

on glass plates. Column chromatography (CCH): silica gel 60 - 200 (Merck). Most often used eluent:

petrol ether/ethyl acetate (PE:EA). - Melting points are uncorrected.

Materials. Thiobenzophenone (2a);47 adarnantanethione (23);” thiofenchone (47);60 selenofen-

chone (48).61

4,4’-Dichlorothiobenzophenone (2b), from the ketone with Lawesson’s reagent; distillation at

200 “C (bath)/O.OOs mm and recrystallization from toluene/pentane 1:l gave 77% of blue crystals, mp

98-100 “C (99-101 OC).62 l3 C NMR: 6 128.3, 130.4 (2 d, 4 arom. CH), 138.4, 145.1 (2 s, 4 arom. C,),

234.1 (s, CS).

2,2-DipherzyW~iirane (38) was prepared from 2a with dimethyloxosuifonium methylide,63 60% of

pure 38. The reported slow decomposition at room temp. (fast on heating) furnishing l,l-diphenylethy-

lene and elementary sulfur can be confirmed. However, with each recrystallization from pentane

(dissolving at room temp., cooling to -20°C) the stability grew. With the best specimen, mp 43.5-44 “C

(39-42 oC),63 the melt no longer became turbid by precipitation of S, (see Section on kinetics).

l,Z,CTrithiolunes as Sources of Zhione S-Sulfdes

3,3,5,5-Tetraphenyl-1,2,4-trithiolane (la). Procedure A (modified from ref. 10): 18.4 g (92.8

mmol) of 2a and 7.59 g (30.9 mmol) of tetrachloro-1,2-benzoquinone (4) in 120 mL of dry ether were

reacted under N, in the dark at 2 “C; after 1 d, la began to precipitate. After 28 d, la was filtered, dis-

solved in little THF, diluted with 3-fold the volume of pentane and stored at -20 “C: 9.72 g (73%) of co-

lorless la, mp 128 ’ C (dec, dark-blue; 128 oC,lo 122-124 “C s6). The benzodioxole 5 remained in the

mother liquor.

Procedure B: 4.76 g (24.0 mmol) of 2a and 2.12 g (9.99 mmol) of 2,2_diphenylthiirane (38) in 40

mL of pentane were stored at r.t. in the dark; crystallization of la started 12 h later. After 24 d the solu-

tion was cooled to -20 “C for 12 h; 3.94 g (92%) of la in coarse crystals, still tinted light-blue , with mp

124.5125 “C (dec); recryst. as above. The mother liquor, after evaporation, was subjected to ‘H NMR

analysis (CDCI,) with a weighed amount of as-TC as standard: 9.18 mmol (92%) of 41 (2H-s at 6 5.41)

and 0.30 mmol (3%) of unreacted 38. - 13C-NMR: 6 92.6 (s, C-3 + C-5); 127.7, 127.9, 129.0 (3 d, 20

arom. CH), 142.3 (s, 4 arom. C&

3,3,5,5-Tetra-(4-chlorophenyl)-1,2,4-trithiolane (lb). Procedure A: 5.14 g (19.2 mmol) of 2b and

1.57 g (6.38 mmol) of 4 were reacted in 120 mL of dry ether for 28 d at r.t. as described above. Recry-

stallization gave 1.18 g (33%) of lb, mp 130-131 “C (dec, dark-blue). -Procedure B: The reaction of 15.2

g (56.9 mmol) of 2b and 6.04 g (28.4 mmol) of 38 in 50 mL of CHCI, (10 d, r.t.) and work-up as above

gave a blue oil which crystallized from pentane, mp 125-127 “C (dec); recrystallization furnished 10.8 g

(67%) of lb in colorless, fine needles, mp 130-131 “C. - 13C NMR: 6 91.7 (s, C-3 + C-5); 128.5, 130.4

(2 d, 16 arom. CH), 130.4, 140.2 (2 s, 8 arom. CJ. - MS (90 “C); m/z (%): 468 (7.6) [M+ - 3S, tetra-p-

chlorophenylethylene+; 37Cl, 472 : 470 : 468 calcd. 4.7 : 9.7 : 7.6, found 4.7 : 10.0 : 7.61, 266 (87)


[C,,H,Cl,S+, Zb+; 37Cl, 56/58], 235,233, 231 (30, 73, 82) [231 is 2b - Cl; 37C1 + 34S of 231 contribute

30% to 233; the remaining 43% of 233 is 3,6-dichlorofluorenyl+, 20, 37Cl 28/30], 155 (100) [CIC,H,-

C=S+ 37Cl + %S 36/35], 120 (13) 111 (16) [ClC,H,+]. - Anal. calcd for CZ6Ht6C14S3: C 55.13, H 2.85,

S 16.9;; found C 54.78, H 2.68, S 16.97.

Dispiro[fluorene3,3’-(1~,4)-trithiolane-5’,9”-fluorene] (43): 2.71 g (12.8 mmol) of 38 reacted

faster with 5.00 g (25.5 mmol) of thiofluorenone (42) in 25 mL of CHCl, than with 2a; after 1 h under

argon in the dark, the green solution was yellow. The solvent was evaporated after 24 h at r.t., and two

crystallizations from pentane produced 2.92 g (54%) of the off-white 43, mp 185-186 “C (dec, red); a

specimen of “difluoryl trisulfide”, obtained by autoxidation of thiofluorene,64 mp 137-138 “C, has prob-

ably another structure. - 13C NMR: 6 71.1 (s, C-3’ + C-5’); 119.0, 126.4, 127.1, 128.6 (4 d, 16 arom.

CH); 141.5, 143.9 (2 s, 8 arom. Cq). - MS (130 “C); m/z (%): 392 (0.2) [M+ - S], 328 (68) [9,9’-bifluore-

nylidene+, 30; 13C 20/24], 256 (9), 196 (100) [thiofluorenone +, 42+], 164 (13) [C,,H,+], 163 (21), 162

(26) 152 (17) &Ha+, biphenylene+], 98 (17), 97 (16), 76 (10) [C6H4’]. - Anal. calcd for C,,H,,S,: C

73.55, H 3.80, S 22.66; found C 74.09, H 4.05, S 22.62.

Dispiro[adamantane-2~‘-(1~,4)-trithiolane-S’~”-adamantane] (26): 212 mg (1.00 mmol) of 38

and 350 mg (2.10 mmol) of adamantanethione (23) 36 were heated in a sealed tube 1 h at 100 “C. After

adding CDCl, and s-TC to the still light-orange melt, the ‘H NMR analysis indicated 100% of 41 (2H-s,

6 5.41). Crystallization from methanol and once more from CHC13/methanol furnished 291 mg (80%)

of colorless 26, mp 191-192°C (189-191 “C; 56 183-185 “C 52 ). - IR (KBr): ? 1450 cm-’ (6 CH,), 2853,

2908 (C-H). - 13C NMR: 6 26.6, 27.0 (2 d, 4 CH); 36.7, 37.3, 38.0 (3 t, nearly ratio 2:2:1, 10 CH,), 39.4

(d, 4 CH), 90.3 (s, C-3’ + C-5’). - MS (140 “C); m/z (%): 364 (28) [M+; 13C 6.3/6.5; 34S + 13C2,

4.4/4.2], 300 (8.9) [M+ - 2S, C,,H,S+, 28; 13C 2.0/2.0], 198 (100) [C,uHt4S2+, 25+; 13C ll/lO; 34S

8.9/7.4], 166 (32) [C,uHi4S+, 23+; t3C 3.6/4.8, 34S 1.4/1.7], 133 (25) [23+ - SH, C,,H,,+], 91 (12)

[tropylium]. - Anal. calcd for C,H,S,: C 65.88, H 7.74, S 26.83; found C 65.77, H 7.98, S 26.43.

4,4’-Diphenylspiro[adamantane-Z~’-(1,3)-dithiolane] (45). a) 1.79 mmol of 23, 0.657 mmol of

38, and 0.661 mmol of as-TC were reacted in 2 mL of CDCl, (contained trace of DCl) in a sealed tube

12 h at 80 “C. ‘H NMR analysis indicated 0.61 mmol (93%) of 45 (s, 6 3.91, 5-H,) and 0.046 mmol

(7%) of 41 (s, 6 5.41, CH,). Isolated were 0.29 mmol of trimeric 23, colorless needles, mp 351-352 “C

dec (345 “C dec).% From the mother liquor, 45 was obtained, mp 125-126 “C (126-128 0C);35 the iden-

tity of the MS was shown. - b) 2.17 mmol of 23, 0.613 mmol of 38, and 0.065 mmol of trifluoroacetic

acid in 2 mL of C,D, were heated in a sealed tube 24 h to 80 “C; the analysis with as-TC showed 0.364

mmol of 41, 0.061 mmol of 38,0.160 mmol of 45; 0.425 mmol of trimeric 23.

TICone S-Sulfirles and Activated Acetylenes

Dimethyl 3,3-diphenyl-3H-l,2-dithiole-4,5-dicarboxylate (6a). a) 428 mg (1.00 mmol) of la and

315 mg (2.22 mmol) of dimethyl acetylenedicarboxylate (DMAD) in 2 mL of CHCl, were refluxed; the

solution turned blue after 10 min and was light-green after 24 h. PLC (PE:EA 5:l) afforded 221 mg

(59%) of 6a (RF 0.52) and 319 mg (94%) of 8a (RF 0.39). Light-yellow crystals of 6a, mp 104 “C, were

obtained from hexane. - b) 0.516 mmol of la and 2.03 mm01 of DMAD were reacted without solvent for

4 h at 60 “C. After removal of the excess of DMAD at 0.01 Torr, ‘H NMR analysis with s-TC indicated


0.428 mmol (83%) of 6a (s, 6 3.41, CH,) and 0.351 mmol (68%) of Sa (s, 6 5.14, 1-H). - UV/Vis: 392

(3.01), shoulder 272 (3.57). - ‘H NMR: 6 3.41, 3.78 (2 s, 2 CH,), 7.10-7.65 (m, 10 arom. H). - 13C

NMR: S 52.3, 53.2 (2 q, 2 OCH,), 80.2 (s, C-3), 127.8, 128.2, 129.2 (3 d, 10 arom. CH), 139.7 (s, 2 arom.

C,); 139.5, 141.1 (2 s, C-4, C-5); 161.1, 164.3 (2 s, 2 CO). - MS (80 “C); m/z (%): 372 (10) [M+, 15a; 13C

2.1/2.3; 34S 0.9/1.2], 308 (100) [M+ - 2 S, 17a; 13C 21.3/21.9], 295 (7) [M+ - C,H,, 19a; 13C 1.1/1.2; 34S

0.6/0.8], 276 (78) [308 - CH,OH, C,,H,,03+, high resol. calcd 276.078, found 276.068, 211, 249 (95)

[Ct7Ht302+, 22a; 13C 18.1/18.6], 232 (15), 221 (19) 219 (22) [C,eHllO+, 249 - CH,O; 13C 3.9/3.9],

218 (28) [249 - CH,O], 205 (37) [C15H,0+], 189 (48) [Ct5H9+, 9-ethylfluorenyl+], 165 (8) [C,,H,+,

201, 121 (5) [C,H,-C&j+], 94 (13), 59 (10) [CH,O-GO+]. - Anal. calcd for C,9H,604S,: C 61.27, H

4.33, S 17.22; found C 61.36, H 4.35, S 17.28.

Dimethyl 2-henzhydrylsuccinate (9): a) 1.30 g (3.49 mmol) of 6a and ca. 15 g freshly prepared

Raney nickel 65 were refluxed in 100 ml of dry benzene under H,. PLC (PE:EA 3:l) of the colorless oil

gave 822 mg (75%) of 9 as the second fraction (RF 0.52) mp 105-106 “C (hexane). - ‘H NMR: 6 2.25-

2.93 (m, 3-H,, diastereotopic); 3.34, 3.54 (2 s, 2 OCH,), 3.75 (dd, 2-H), 4.03 (d, benzhydryl-H); 7.21,

7.25 (2 br s, 10 arom. H). - 13C NMR: 6 35.9 (t, C-3), 46.5 (d, C-2); 51.6, 51.7 (2 q, 2 OCH,), 54.3 (d,

benzhydryl-CH); 126.7, 126.9, 127.8, 128.1, 128.4, 128.9 (6 d, 2 diastereotopic CeHs); 141.1, 141.6 (2 s, 2

arom. C,); 171.9, 174.4 (2 s, 2 CO). - MS (80 “C); m/z (%): 312 (22) [M+; 13C 4.6/4.4], 280 (11) [M+ -

CH,OH], 252 (54) [M+ - HCO,CH,; 13C 10/9], 221 (18) [C,,H,,O+], 193 (21) [C,,H,O+, lo-an-

thronyl+; 13C 3.3/3.8], 167 (100) [benzhydryl+], 165 (26) [fluorenyl+, 201, 152 (13) [C,,H,+, biphe-

nylene+]. - Anal. calcd for C,,H,O,: C 73.06, H 6.45; found C 72.86, H 6.24.

b) Methyl 2-carboxymethylvinylacetic ester (10) was prepared from dimethyl succinate, benzophe-

none, and sodium hydride in ether, 37%, mp 126-127 “C, by the procedure given for diethyl succinate.@’

Anal. calcd for C18H1604: C 72.96, H 5.44; found C 72.88, H 5.26. - 2.96 g (10.0 mmol) of 10 in 70 mL

of methanol were shaken with 0.5 g Pd-C (5%) under HZ; after 16 h 235 mL H, were consumed. Freed

from catalyst and solvent, the half-ester was treated in THF with ethereal diazomethane. Recrystalliza-

tion from hexane gave 2.53 g (85%) of 9 identical in mixed mp and 13C NMR spectrum with the above

specimen.

Dimethyl 3,3-di(4-chIorophenyI)-3~-l~-dithiole-3,4-dicar~~late (6b). a) 520 mg (0.92 mmol)

of lb and 286 mg (2.01 mmol) of DMAD in 1 mL of CHCl, were refluxed for 18 h; the blue color of 2b

appeared after 5 min, and the solution was deep-red after 18 h. The usual work-up with PLC (PE:EA

5:l) gave 203 mg (50%) of 6b (RF 0.50) and 231 mg (56%) of Sb (RF 0.36). The lustrous, light-yellow

crystals of 6b (hexane) had mp 110-l 11 “C. - b) 0.408 mm01 of lb and 4.05 mmol of DMAD were heated

for 4 h to 60°C. The ‘H NMR integrals were compared with that of s-TC and pointed to 0.277 mmol

(68%) of 6b (s, b 3.49, CH,) and 0.294 mmol (72%) of 8b (s, 6 5.11, 1-H). - UV/Vis: 391 (3.05) in-

flection 275 (3.69). - ‘H NMR: 6 3.49,3.81 (2 s, 2 OCH,), 7.20-7.55 (AA’BB’ of 2 C,H,). - 13C NMR: 6

52.6, 53.3 (2 q, 2 OCH,), 79.1 (s, C-3); 128.3, 130.6 (2 d, 8 arom. CH); 134.6, 137.9 (2 s, 4 arom. C );

138.4, 142.1 (2 s, C-4, C-5); 161.1, 164.2 (2 s, 2 CO). - MS (130 “C); m/z (%): 440 (21) [M+, 15b; 12 C

4.4/4.0; 37Cl + 34 S 15/16], 409 (5) [M+ - OCH,; 37Cl + 34S 3.8/3.7], 381 (5) [M+ - CO,CH,; 13C

1.0/1.2; 37C1 + ?5 3.7/3.7], 376 (6) [M - 2S, 17b], 347 (23), 344 (100) [C,,H,,Cl,O,+, 21, X = Cl; 13C

20121; 37Cl + 13C2 66/69], 329 (12) [M+ - C,H,Cl, 19b; t3C 1.8/1.7; 37Cl + 34S 4.4/5.1], 317 (15)

[C,,H,,Cl,O,+, 22b; 37Cl 10/12], 223 (12), 189 (11) 155 (7) [ClC,H,-C=S+], 111 (3) [ClC6H4+], 59 (6)


[CH,O-GO+]. - Anal. calcd for Cr9H,,Cl,03S,: C 51.70, H 3.20, S 14.53; found C 51.56, H 3.03, S

14.54.

3,3-Diphenyl-3H-1,2-dithiole-4,5-dicarbonitrile (lla): 3.27 g (7.63 mmol) of la and 1.17 g (15.4

mmol) of dicyanoacetylene 67 in 10 mL of CHCl, were refluxed for 4 h. The light-red solution furnished

after the usual work-up (PE:EA 3:l) 1.77 g (76%) of lla as a deep-yellow oil (RF 0.84) and 1.48 g

(71%) of 13a (RF 0.64); lla crystallized from methanol in yellow needles, mp 132 “C. - IR (KBr): ij 698

cm-r, 706, 744, 760 (C,H, wagg. ), 1633 (C=C), 2218 (C=N). - UV/Vis: 413 (3.43), 295 (3.70). - 13C

NMR: 6 78.6 (s, C-3), 109.9, 112.9 (2 s, 2 CN); 125.0, 128.1 (2 s, C-4 + C-5); 128.1, 129.01 129.6 (3 d, 10

arom. CH), 137.5 (s, 2 arom. CJ. The signal of C-4 at 128.1 is only recognizable in the off-resonance

spectrum due to superposition. - MS (90 “C); m/z (%): 306 (17) [M+, 15a; 13C 3.2/3.6; ?S 1.5/1.6], 274

(3) [M+ - S, 16a], 242 (100) [M+ - 2S, 17a; 13C 19/20], 229 (13) [MC - C,H,, 19a; 13C 1.6/1.7, 34S

1.2/1.1], 214 (13) [C,,H,N+, NC-C=C-fluorenyl+], 165 (6) [fluorenyl+, 20; 13C 0.8/0.9], 121 (4) [C6HS-

C=S+], 77 (12) [C6Hs+], 64 (7) [S,; 34S 0.58/0.63]. - Anal. calcd for C,,H,,N,S: C 66.64, H 3.29, N 9.14,

S 20.93; found C 66.59, H 3.30, N 9.08, S 20.99.

3,3-Di(4-chlorophenyI)-3~-l~-dithiole-4,S-dicar~nitrile (llb): The 1:2 reaction of lb and

dicyanoacetylene (4 h in refluxing CHCI,) provided 27% of llb (RF 0.85) as deep-yellow oil and 75%

of 13b (RF 0.64) in light-yellow crystals, mp 173-174 “C. llb is unstable at r.t. and could neither be ob-

tained crystalline nor analytically pure. - 13C NMR: 6 77.4 (C-3); 09. 1 6. 112.6 (2 s, 2 CN); 124.1, 128.2

(2 s, C-4 t C-5); 129.4, 129.5 (2 d, 8 arom. CH); 135.6, 136.2 (2 s, 4 arom. CJ.

4,5,6,7,8,9-Hexahydro-3~-diphenyl-3H-cycloocta-l~-dithio~e (1Za): 430 mg (1.00 mmol) of la

and 520 mg (4.82 mmol) of cyclooctyne 68 were heated 4 h at 60 “C without solvent; the color changed

to blue and green to yellow. Quantitat. ‘H NMR analysis (CDCl,, s-TC as standard) disclosed 98% of

14a (s, 6 4.95, 1-H); there was no specific signal for 12a. Work-up led to 224 mg (66%) of 12a in

coarse, yellow crystals, mp 108 “C. - IR (KBr): < 687 cm-r, 697, 739, 755 (C,H, wagg.), 1625 (C,H,

vibr.), 1653 (C=C). - UV/Vis: 373 (2.33). - ‘H NMR: 6 0.47 - 0.83 (m, CH,), 1.11 - 1.90 (m, 3 CH,),

2.06-2.55 (m, 2 CH,, allylic), 7.1-7.6 (m, 2 C,H,). - 13C NMR: 6 26.0, 29.1 (2 t, 4 CH& 28.8, 30.0 (2 t, 2

CH,); 83.1 (s, C-l); 127.3, 127.9, 129.2 (3 d, 10 arom. CH), 132.6, 136.4 (2 s, C-3a t C-9a), 143.5 (s, 2

arom. Cs). - MS (20 eV, 70 “C); m/r (%): 338 (1.8) [M+, 15a; 13C 0.42/0.44, 34S t 13C2 0.21/0.20], 306

(4.4) [M+ - S, 16a; 13C 1.0/0.9], 274 (58) [Mt - 2S, 17a; 13C 14/13], 272 (100) [M - 2s - 2H; 13C 24/25],

261 (2) [M+ - C,H,, 19a], 244 (22) [272 - 2 CH, 1,204 (21) , 192 (14) 165 (10) [fluorenyl+], 64 (1)

[S2’ ?]. - Anal. calcd for C,,H,S,: C 74.50, H 6.55, S 18.95; found C 74.63, H 6.86, S 19.01.

4,5,6,7,8,9-Hexahydro-3,3-di(4-chlorphenyl)-cycloocta-l~-dithiole (12b): 252 mg (0.445 mmol) of

lb and 402 mg (3.72 mmol) of cyclooctyne were heated 4 h at 60 “C; ‘H NMR analysis indicated 91% of

14b. Separation was achieved by PLC, first with PE:EA lO:l, and subsequently with cyclohexane; 12b, a

yellow oil (99.3 mg, 55%), was not obtained crystalline. - UV/Vis: 322 (3.14). - ‘H NMR: 6 0.52-2.53 (3

m 1:3:2, 6 CH,), 6.8-7.6 (m, 2 C,H,). - 13C NMR: 6 25.9, 26.0, 29.0, 30.0 (4 t, 4 CH,), 28.8 (t, 2 CH,);

81.7 (s, C-3); 128.2, 130.5 (2 d, 8 arom. CH); 131.9, 133.5, 137.4, 141.6 (4 d, 4 arom. C,, C-3a, C-9a). -

MS (90 “C); m/z (%): 406 (21) [M+, 15b; 37Cl t 34S E/17, 13C 5/6], 374 (5) [M+ - S, 16b], 342 (45)

[M+ - 2S, 17b; 37C1 27/29], 340 (4) [342 - 2H], 307 (17) [342 - Cl; 37Cl 5.0/5.3], 295 (20) [M+ - C,H,Cl,

19b; 37Cl t ?S 8.1/8.4], 85 (84) [C6H13+], 43 (59) [C3H7+], 41 (100) [C3Hs+]. - Anal. calcd for


C,,H,,-&S,: C 61.91, H 4.95, S 15.74; found C 62.03, H 5.29, S 15.73.

Trithiolancs and Thiones - Metathesis

5’,5’-Diphenylspiro[adamantane-2,3’-(1Z,4)-trithiolane] (24a): 1.86 g (4.34 mmol) of la and

1.01 g (6.07 mmol) of 23 in 5 mL of CHCl, were refluxed under argon for 4 h; after 2 min the blue color

of 2a appeared. The solvent was removed and the deep blue oil dissolved in 20 mL of pentane: 1.39 g

(81%) of 24a in light-blue crystals, mp 129-131 “C (dec); from THF-pentane 1:3 at -20 “C 1.17 g of 24a

was obtained in colorless needles, mp 131-132 “C (dec, blue). - IR (KBr): 3 690 cm-‘, 721, 744, 752

(C,H, wagg.); 1444, 1489 (ring vibr.). - 13C NMR: C, symmetry reduces the adamantane signals to 3 t, 3

d, 1 s. 6 26.5, 26.7 (2 d, C-5, C-7), 36.7 (t, C-6), 37.7 (t, C-4 and C-9 coincide with C-8 and C-10) 39.8

(d, C-l/C-3), 89.3 (s, C-3’), 93.7 (s, C-5’); 127.5, 127.8, 128.9 (3 d, 10 arom. CH), 142.4 (s, 2 arom. CJ. -

MS (110 “C); m/i (%): 396 (2.7) [M+; 13C 0.69/0.63; 3jS + 13C2, 0.44/0.43], 332 (16) [M+ - 2S, 27, Ar

= C,H,; 13c 4.0/3.9; 34S + 13C2 1.2/1.2], 231 (2.9) [t3C of 230 and ?S of 229, calcd 2.91, 230 (13)

[C,3%clS2 + 9 7a+; ?S 1.2/1.2], 229 (12) [C13H9S2+, fluorenyl-SSH+], 198 (69) [2a+; 13C 10.2/10.8; 34S

+ 13C2, 3.8/3.8], 166 (100) [C,uHt4St, 23+], 165 (83) [Ct3H9+, fluorenyl+, 20, X = H], 133 (18) [166 -

SH. 13C 2.0/2.2], 121 (48) [C,H&=S+], 105 (9) [methyltropylium+], 91 (34) [tropylium], 77 (24)

(Cg)H5+]. Anal. calcd for Cz3Hz4S3: C 69.65, H 6.10, S 24.25; found C 69.75, H 6.01, S 24.32.

5’,5’-Di(4-chlorophenyl)spiro[adamantane-2,3’-(1~,4)-trithiolane] (24b): From lb and 23 by the

above procedure 83% of 24b were obtained, colorless needles, mp 124-125 “C (dec, slowly blue). - ‘H

NMR: 6 1.47-2.55 (m, 14 Ad-H), 7.1-7.6 (AA’BB’ of 2 C,H,). - 13C NMR: 6 26.5, 26.7 (2 d, C-5, C-7),

37.6 (t, C-6); 36.7, 37.8 (2 t, C-4/C-9, C-8/C-10), 39.9 (d, C-l/C-3), 88.0 (s, C-3’), 94.4 (s, C-5’); 128.1,

130.3 (2 d, 8 arom. CH); 133.8, 140.6 (2 s, 4 arom. CJ. MS (190 “C); m/z (%): 464 (1.3) [M+; t3C

0.34/0.32; 34S + 37C1, 1.03/1.05], 400 (7) [M+ - 2s; 27; 13C 1.8/1.9; 35Cl + 34S 4.8/5.0], 298 (6)

[Ct3H8C1,S,+ > , 7b+ 35C1 + 34S, 4.4/4.6], 266 (79) [2b+; 37Cl + 34S 541551, 233 (67) [40% 3,6-dichlo-

rofluorenyl+ + 27% (35C1 + 34S) of 231; 35C1 of dichlorofluorenyl+, 20, 26/27], 231 (76) [2b+ - Cl; 13C

lW31, 198 (18) [C,,H,,S,+, 25+], 166 (100) [C,t,H14S+, 23+; 13C 11/12; 34S + 13C2 5.0/4.8], 155 (90)

[ClC,H,-C=S+; 34S + 35Cl, 33/32], 133 (21) [C,uHi3+], 124 (18), 111 (21) [C1C6H4+], 91 (40)

[tropylium]. - Anal. calcd for C,3H,,Cl,S3: C 59.34, H 4.76, S 20.67; found C 59.26, H 4.75, S 20.72.

Dispiro[adamantane-2,3’-(1~,4)-trithiolane-5’Z”-adamantane] (26): 400 mg (1.01 mmol) of 24a

and 600 mg (3.6 mmol) of 23 in a sealed tube were heated to 130 “C for 30 min; the clear orange melt

turned deep-blue after 2 min. From CHC13-methanol crystallized 206 mg (56%) of colorless 26, mp

191-192 “C; mixed mp with the specimen prepared from 23 and 38 showed no depression.

Kinetic Studies with 2,2Jhphenylthiirane (38)

Self Decomposition. We described above that the rate of “spontaneous” conversion of 38 to 41

decreased with the purity of 38. The best specimen, 1 M 38 in [D,]DMSO, was sealed in the NMR tube

and kept in the thermostat in the dark except for the brief handling during the ‘H NMR measurements.

For each concentration, the sum of the machine integrals for the 2H-s of 38 (6 3.34) and 41 (b 5.55)

was set to 100 and split according to the ratio. The conversion was followed up to 35% (after 86.8 d) at

23.0 “C, 43.3% (136 h) at 50.5 “C, and 77% (101.4 h) at 60.0 “C. Based on 10 concentration measure-

ments each, the following rate constants, 107k,, and correlation coefficients (r, in brackets) were evalua-


ted from -In AO/At vs. time by linear regression: 0.56 s-l (0.9955) for 23.0 “C, 11.7 se1 (0.9992) for 50.5

“C, 40.0 s-l (0.9999) for 60.0 “C. The first order was strictly obeyed, and the half-life at 34 “C, the temp.

of the sulfur transfer measurements below, was 47.3 d. The k, values may still refer to catalyzed reacti-

ons. The rate constants of sulfur transfer (Table 1) are not corrected for the slow self decomposition.

Rates of Sulfur Transfer. Concentrations and results in Table 1. The desulfurization of 38 by 2a

may serve as an example for the protocol. 755.5 mg of Za, 323.4 mg of 38, and 249.8 mg of as-TC

(standard) were dissolved in CDCl, in a 5 mL volumetric flask at 34 “C: part of the solution, cooled to -

78 “C, was sealed in the NMR tube and immersed in the thermostat at 34.0 “C. The decrease of A (38)

was followed by comparing the machine integral with that of as-TC for 13 concentration measurements

up to 92.4% conversion of A (after 70.6 h). On the basis of the stoichiometry, it was set for the concen-

tration of 2a: B, = B. - 2(A0 - 4). The integrated rate eq. for the second order,

1 k,t =

ALlB ___ In - BO-2A0 B,A

is fulfilled as illustrated in Figure 1. Linear regression furnished lo5 k, = 2.91 Melsel with r = 0.9982.

For triphenylphosphane, B, = A, was chosen, and the integrated rate eq. simplified to k,t =

l/A, - l/AO; 15 concentration measurements. The runs with 47 and 48 followed the first-order law; the

k, Jr was divided by the catalyst concentration.

Acknowledgments

We express our gratitude to the Fonds der Chemischen Industrie for support. Our thanks are

going to Professor H.-F. Grtitzmacher, University of Bielefeld, for kind advice. We thank Helmut Huber

for his help in the NMR measurements, Reinhard Seidl for the MS, and Helmut Schulz for the micro-

analyses.

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(Received in Germany 18 October 1996; uccepted 1.5 November 1996)

1,3-dipolar cycloadditions, 98 the chemistry of thiocarbonyl s-sulfides

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