8 Ylides and Related Compounds

BY S. TRIPPETT

1 Methylenephosphoranes

Preparation.-The preparation of methylenephosphoranes has been reviewed.l Pure methylenetriphenylphosphorane has been obtained as shown in Scheme 1, together with the pure trimethylsilylmethylene- and bis(trimethylsilyl)methylene-phosphoranes.2

Ph3P: CH, 85%

+ ii Ph,PMe Br- ----+ Me4; Br-J. + Ph,P: CH,

82% I I iii

iV + Me4$ Br-J. + Ph,P: CH. SiMe, -----+= P$P. CH(SiMe,), Br- 77%, m.p. 12-13 "C

1- Ph,P: C(SiMe,), & [ I

49%, m.p. 139-140 "C

v, BuLi; vi, 270-300 "C, 0.1 mmHg Reagents: i, NaH, THF; ii , Me3P:CH,, ether; iii, Me,P:CH.SiMe,, ether; iv, Me,SiBr;

Scheme 1

Further examples have appeared of the use of epoxides as the source of the base in olefin synthesis, among them the synthesis of crocetin dialdehyde (1) shown in Scheme 2., Additional polymeric Wittig reagents have been described and used in olefin ~ynthesis.~ 1 H. J. Bestmann and R. Zimmermann, Fortschr. Chern. Forsch., 1971, 20, 1.

H. Schmidbaur, H. Stuhler, and W. Vornberger, Chem. Ber., 1972, 105, 1085. 3 G.P. 2 037 935-6 (Chem. Abs., 1971, 75, 20 707, 49 365). 4 S. V. McKinley and J. W. Rakshys, jun., J . C . S. Chem. Comm., 1972, 134; W. Heitz

and R. Michel, Angew. Chem. Internat. Edn., 1972, 11, 298.

176

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Ylides and Related Compounds 177

I

( 1 )

0 / \

Reagents: i, MeCH,CH-CH,, CH,Cl,, 75 "C

Scheme 2

Phosphines and the imine (2) gave the stable ylides (3).5

R3P + PhCH: CH-N: C(CF3)Z - R3P: CPh- CH: N - CH(CF3), (2) R = Ph or Pri (3)

The equilibrium established between methylenetriphenylphosphorane and ethyltriphenylphosphonium bromide in THF has been investigated by quenching with benzaldehyde.

Ph3P: CH2 + Ph3PEt Br- 7 Ph3$Me Br- + Ph3P: CHMe +

15:l

Reactions.-Halides. The stable ylides (4) are C-alkylated by p-nitrobenzyl bromide.' Methyl and ethyl iodides alkylate the formyl- stabilized ylides ( 5 ) exclusively on oxygen8 to give mixtures of cis- and trans-isomers not necessarily in ratios corresponding to the isomer compositions of the ylides. Dibromo- and di-iodo-methane gave the bisphosphonium salts (6).

2 Ph3P: CH- C 0 . R + p-NO,. C,H,. CH,Br - (4; R = OEt or Ac)

+ Ph3P: C(CO.R).CH,.C,H,.NO,-p + Ph,P.CH,.CO*R Br-

Methylenetriphenylphosphorane with 1 ,Zdibromopropane gave @ the cyclobutylphosphonium salt (7), which was used in olefin synthesis. The

K. Burger, J. Fehn, J. Albanbauer, and J. Friedl, Angew. Chem. Internat. Edn., 1972,11, 319. A. Piskala, M. Zimmermann, G. Fouquet, and M. Schlosser, Coll. Czech. Chem. Comm., 1971,36,1482. M. I. Shevchuk, A. F. Tolochko, and A. V. Dombrovskii, J. Gen. Chem. (U.S.S.R.), 1971, 41, 534. C. J. Devlin and B. J. Walker, Tetrahedron Letters, 1971, 4923. J. E. Baldwin and R. H. Fleming, J. Amer. Chem. Soc., 1972, 94,2140.

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178 Organophosphorus Chemistry

stable a-chloro-ylides ( 8 ) were obtained as shown.lo

R’ ‘OMe

PPh,

2 Ph,P:CH, + McCHBr.CH,Br Br-

Ph3kH,CO*R C1- + p-Me *C6H,.S0,.NHCI - + Ph,P:CCI*CO*R

R = OMc, OEt, Me, or Ph (8) > 70;/,

Carbonyls. The stable ylides (9) react with a-diketones to givell the 1,4-diketones (10). The allenic ketones (11) have been shown12 to be intermediates in the formation of 4-pyrans from diphenylketen and the ylides (9).

The acridinium betaines (1 3) were formed l3 from the 2-amino- naphthoquinones (1 2) and arylidenephosphoranes under vigorous con- ditions, oxidation or disproportionation occurring at some stage.

Wittig olefin syntheses in hydroxylic solvents may proceed via vinyl- phosphonium salts (14) and not via the usual oxaphosphetans when the double bond formed is stabilized by a n-bonding substituent.14 In some

(9) R1 = Me or Ph

10 H. J. Bestmann and R. Armsen, Synthesis, 1970, 590. 11 E. Ritchie and W. C. Taylor, Austral. J . Chem., 1971, 24, 2137. 12 M. Duprt and H. Strzelecka, Cumpt. rend., 1972, 274, C, 1091. lS H. J. Bestmann, H. J. Lang, and W. Distler, Angew. Chem. Internat. Edn., 1972, 11,59. 14 E. E. Schweizer, D. M. Crouse, T. Minami, and A. T. Wehman, Chem. Cumm., 1971,

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YIides and Related Compounds 179

(13) 11-46x

cases, e.g. (15), the vinylphosphonium salt may be isolated. However, the optically active benzylphosphonium salt (1 6) with benzaldehyde and ethanolic sodium ethoxide gives16 the oxide (17) with almost complete retention of configuration at phosphorus, and the vinylphosphonium salt

Ph,P:CHR' + R 2 R 3 C 0 e- Ph,6-CHR1.C(0)R2R3

Ph,;*CR': CR2R3 HO- - Ph,6*CHR1.C(OH)R2R3 R40-

(14)

I Ph,PO + R'CH:CR2R3

+ PPh, Br-

+ Ph3P.CH2CH:CH2 + Br- - E t o H o z k * C H : C H 2

EtOH M e E t P h k H , P h Br- + PhCHO EIONa+ Me Et PhPO + PhCH:CHPh

MeEtPh6CPh:CHPh

(16) (17)

(18)

l* D. J. H. Smith and S. Trippett, J. C. 5'. Chem. Comm., 1972, 191.

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180 Organophosphorus Chemistry

f

+

I

t s3 (18) is therefore unlikely to be an intermediate unless it undergoes alkaline hydrolysis with complete retention of configuration at phosphorus. Vinyl- phosphonium salts have also been implicated in the complex reactions occurring when 2-hydroxyalkylphosphonium salts are treated with base in hydroxylic solvents,16 and l7 in the previously observed formation of the ethers (20) and (21) from the salt (19) and sodium methoxide.

The stereospecificity of the /%oxido-ylide synthesis using formaldehyde as one of the aldehyde components is dependent on the order of use of the a1deh~des.l~ Thus, starting from the ethylidenephosphorane, use of hexaldehyde and paraformaldehyde in that order gave almost pure isomer (22), while their use in the reverse order gave a mixture of the isomers (22) and (23) in the ratio 36 : 64.

16 J. W. Rakshys, jun., and S. V. McKinley, Chem. Comm., 1971, 1336. 1' E. E. Schweizer, T. Minami, and D . M. Crouse, J , Org . Chem., 1971, 36, 4028.

E. E. Schweizer, C. J. Berninger, D. M. Crouse, R. A. Davis, and R. S. Logothetis, J. Org. Chem., 1969, 34, 207.

l9 M. Schlosser and D. Coffinet, Synthesis, 1971, 380.

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Ylides and Related Compounds 181

C5H11 CH,OH \ I

Ph,P:CHMe .'

The unexpected formation of ethyl a-safranate (26) from allylidenetri- phenylphosphorane and the keto-ester (24) could involve coupling between the y-carbon of the ylide and the /I-carbon of the unsaturated ketone to give the betaine (25), followed by proton transfer and an intramolecular

X C 0 2 E I ~ R 0 2 E t Ph,P:CH-CH:CH, +

0 f - (24) (25)

Ph,P+

Ph,P

C0,Me

M ~ o - > M e 0

R I i

(28)

PIi,,P: Ct I M C 1 MeoHMe R

C0,Me

(29) H

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182 Organophosphorus Chemistry

Wittig reaction.20 Among other unusual olefin syntheses is the formation 21

of the six-membered olefin (29) from the five-membered ketone (27) and an excess of ethylidenephosphorane in DMSO. This probably involves initial base-catalysed isomerization of (27) to the six-membered ketone (28).

A full account has appeared22 of the use of ylides in the synthesis of cyclopropyl-substituted ethylenes. Among unsuccessful Wittig reactions noted is the failure of cyclohexylidenetriphenylphosphorane to give the olefin (30) on reaction with cycl~hexanone.~~

Ph,P :CCI, + PI1C0.CN - PhC(CN):CCI, (31) 73;!

A full account has appeared 24 of the reactions of polyhalogenoacroleins, keto-acetals, ethyl pyruvate, and various halogenated unsaturated ketones with dichloro- and dibromo-methylenetriphenylphosphoranes generated in situ. This dichloro-ylide reacted 25 with the carbonyl of benzoyl cyanide in a normal olefin synthesis to give the unsaturated nitrile (31).

+ Ph,P:CHR ---+

R 0 0 R I4 + RR H H

*OonC

(32) R = CO,E1 o r CN

(33) (34)

2 o G. Biichi and H. Wiiest, Helu. Chim. Acta, 1971, 54, 1767. 21 E. G. Brain, F. Cassidy, A. W. Lake, P. J. Cox, and G. A. Sim, J. C. S. Chem. Comm.,

1972,497. T . Teraji, I. Moritani, E. Tsuda, and S. Nishida, J . Chem. SOC. (C) , 1971, 3252.

23 J. B. Jones and P. W. Marr, Canad. J. Chem., 1970, 49, 1300. 24 C. Raulet and E. Levas, Bull. SOC. chim. France, 1971, 2598. 26 R. L. Soulen, D. B. Clifford, F. F. Crim, and J. A. Johnston, J. Org. Chem., 1971,36,

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Ylides and Related Compounds 183

The bicyclic imide (32) reacted under vigorous conditions with stable ylides to give mixtures of the mono- and bis-olefins.26 The homologue (33) behaved similarly but no reaction was observed with (34). The sulphon- amide (35) reacted normally 27 under vigorous conditions.

Whereas the ester ylide (36; R = OEt) with N-p-nitrobenzoylaziridine gave the ylide (38) by proton transfer in the intermediate (37), the aroyl ylides (36; R = Ar') catalysed the conversion of the aziridine into the oxazoline (39), presumably uia the same type of intermediate.28

Ph,P:CHCO- R + A r C O - N l --+ Ph,kH(CO-R)CH,CH2NCO-Ar

(36)

Ph,P:C(CO, Et).CH,CH,N HCO-Ar

(38) R = At'

J.

Ar = p-NO,.C,;H, Ph,P:CHCO.Ar' + Ar

(39)

Among other carbonyl compounds successfully used in olefin synthesis are (40),29 (41),30 the optically active dione (42),31 the pyrroles (43),32 and the xanthone (44).33 In the last case the aldehyde was added rapidly to a large excess of the ylide, followed immediately by acetone to remove the excess reagent.

Miscellaneous. The unusual reductions of benzyltriphenylphosphonium salts with sodium to give benzyldiphenylphosphine have been shown 34 to involve reduction of the benzylidenephosphorane. This ylide with sulphur in benzene at 70 "C gave 36 triphenylphosphine sulphide, a pentasulphide formulated as (45) or (46), and only traces of isomeric stilbenes. Previous workers 36 reported high yields of stilbenes from the same reaction carried out in refluxing toluene. Benzoylmethylenetriphenylphosphorane (47) with sulphur gave a polymer of the thioaldehyde (48). 2o W. Flitsch and B. Muter, Chem. Ber., 1971, 104, 2852. 27 M. Natsume, M. Takahashi, K. Kiuchi, and H. Sugaya, Chem. and Pharm. Bull.

(Japan), 1971, 19,2648. 28 H. W. Heine and G. D. Wachob, J. Org. Chem., 1972, 37, 1049. gs N. N. Belyaev and M. D. Stadnichuk, J. Gen. Chem. (U.S.S.R.), 1971, 41, 1888. 30 L. D. Quin, J. W. Russell, jun., R. D. Prince, and H. E. Shook, jun., J. Org. Chem.,

1971,36, 1495. D. A. Lightener and G. D. Christiansen, Tetrahedron Letters, 1972, 883.

32 W. Flitsch and U. Neumann, Chem. Ber., 1971, 104, 2170. 33 H. D. Locksley, A. J. Quillinan, and F. Scheinmann, J. Chem. SOC. (C) , 1971, 3804. 34 A. W. Herriott, Tetrahedron Letters, 1971, 2547. 35 H. Tokunaga, K. Akiba, and N. Inamoto, Bull. Chem. SOC. Japan, 1972, 45, 506. 36 H. Magerlein and G. Meyer, Chem. Ber., 1970, 103, 2995.

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184

R S i C H:C H a C HO

(40)

Organophosphorus Chemistry

0

("I P

Me

O C 0 - R ' N + Ph,P:CR'*CO,Et

H 0

(43)

4 6'X (44)

S / \

\ / s.s.s.s

(45) 14:;

Ph,P:CHPh + S8 Ph,,PS + PhCH CIIPh

83;;

Ph,P:CHCO*Ph + s 8 + Ph,,PS 4- (PhCO-CHS),

(47) (48)

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Ylides and Related Compounds 185

Lithiation of the phosphorane (47) in benzene in the presence of HMPT gave 37 a solution containing the 'enolate ylide' (49), which on prolonged refluxing with ketones gave, after work-up, the ,€+unsaturated ketones (50).

(47) Li Ph,P:C:C(OLi)Ph

(49)

R'CH:CR2. CH2CO*Ph (50) 3042 : ;

The phosphonium acetates (51) are soluble in organic solvents, in contrast to the previously prepared chlorides. With base in methanol they gave the bisphosphoranes (53), from which the divinylmercury compounds (52) were obtained on reaction with aldehydes.38

Ph,P:CHR' + Hg(OAc), - Ph3kHR1*HgOAc AcO-

(51)

McOl1 hasc I K'CHO

R2CH:CR1*Hg*CR':CHR2 C-- Ph,P:CR'*Hg.CR':PPh,

(52) (53)

A full account has appeared3g of the reactions of acyl azides with P-ket o-a1 kylidenephosphoranes. These phosphoranes with ni trile oxides gave isoxazoles (54) 40* 41 and the stable ylides (56) or (57), formed as shown via the quinquecovalent 1 :1 adducts (55).41

The 3-pyrrolines (59) were formed on refluxing the aziridine (58) with the stable ylides Ph,P: CHR (R = CN or C0,Me) in toluene.42 Methylene- triphenylphosphorane with benzoyl isocyanate gave a compound that has been assigned structure (60).43

3' C. Broquet and M. Simalty, Tetrahedron Letters, 1972, 933. 38 N. A. Nesmeyanov, A. V. Kalinin, and 0. A. Reutov, Doklady Chem., 1970,195, 788. 39 P. Ykman, G. L'AbbC, and G. Smets, Tetrahedron, 1971, 27, 5623. 4O T. Sasaki, T. Yoshioka, and Y. Suzuki, Yuki Gosei Kagaku Kyokai Shi, 1970'28,1054

(Chem. Abs., 1971, 74, 125 528). 41 G. L'Abbt, J.-M. Borsus, P. Ykman, and G. Smets, Chem. and Ind., 1971, 1491. 42 F. Texier and R. CarriC, Tetrahedron Letters, 1971, 4163. 43 Y. Ohshiro, Y. Mori, M. Komatsu, and T. Agawa, J. Org. Chem., 1971, 36, 2029.

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186 Organophosphorus Chemistry

0 ;Ph, I I

I \ R’-C-CH

Ph3P:CHC0.R1 f R2CN0 --+ 0, ,,CR2 ---+ : 5 R ’ N N

I (54)

R’COCH-PPh, / \ ~1 = M~ MeCOC:PPh, MeCO -C: PPh:,

I [ PhL:NOH] ---+ PhNHCO R’C* ,o K’= PIl’ N

K’ = K‘ = PI1 - I’1iJ1’0

I’IlJ? CHCO. I’ll

I PhCO.CH:C:NPh Ph,P:C(CO*Ph)-C(NHPh):CHCO.Fh

(57)

I cllu.;, + toliicne

PhCH-C(CO,Mc), + Ph,P:CHR -----+ Ph,PCHR

\ / PhLH C(CO,Mc), \ /

N

N P 11 K = CN or CO,Me

( 5 8 ) Ph

I< OMe PI1,P:CR CO,Mc

4- I I

\ / N P h

PhCH CHC0,Mc

Ph

(59) 70-90‘” , O

0 \\ CO*Ph C -N

j / I

\ / PhCO*NCO + Ph,P:CH, - Ph,P=C C=O + C,H,

,.”-E (60)

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Ylides and Related Compounds 187

The sulphonium chloride (61) reacted with a series of stable phosphoranes to form intermediates from which the sulphonium phosphoranes (63) were formed on hydrolysis and from which the methylthiophosphoranes (62) were obtained on heating.44 The meso-ionic dehydrodithizone (64) with the ester phosphorane gave a compound assigned 45 the betaine structure (65).

h 4 e 2 & b CI- + Ph,P:CHR __f

0 R = CO,Et, Ac, Bz, or CN H 2 0 , KI

(61)

P h P : C R. SMe Ph,P:CR.SMc, I -

(62) (63)

Ph P 11 \ /

Ph Ph \ /

+ Ph,P:CHCO,Et --+ Y -N\

s- (64)

A further account has appeared 46 of the reactions of ylides with nitrosyl chloride, generated in situ from isopropyl nitrite and hydrogen chloride. The synthesis of phosphacyanines 47 has been extended 48 to include the use of vinyl ethers.

2 Phosphoranes of Special Interest

Cyclic phosphonium ylides have been reviewed.4D Ab initio calculations on methylenephosphorane, H2C: PH3, show no barrier to rotation round the CP bond whether or not d-orbitals are included in the calc~lat ions.~~ The energy changes when these orbitals are included are commensurate with p,.-d, feedback.

Details have appeared 51 of the semi-empirical MO calculations on cyclopentadienylidenetriphenylphosphorane (66). A kinetic investigation of the reaction of this phosphorane with tetracyanoethylene in the presence

44 E. Vilsmaier, W. Spruegel, and W. Boehm, Synthesis, 1971, 431. O5 P. Rajagopalan and P. Penev, Chem. Comm., 1971, 490. 46 M. I. Shevchuk, E. M. Volynskaya, and A. V. Dombrovskii, J. Gen. Chem. (U.S.S.R.),

1971, 41,2019. 47 A. V. Kazymov, E. B. Sumskaya, K. M. Kirizlova, and E. P. Shchelkina, J. Gen. Chem.

(U.S.S.R.), 1971, 41, 2459. 48 H. Depoorter, J. Nys, and A. Van Dormael, Bull. SOC. chim. belges, 1964, 73, 939. 49 M. Davies and A. N. Hughes, J . Heterocyclic Chem., 1972, 9, 1. 5 0 I. Absar and J. R. Van Wazer, J . Amer. Chem. SOC., 1972, 94, 2382. 51 K. Iwata, S. Yoneda, and Z . Yoshida, J. Amer. Chem. SOC., 1971, 93, 6745.

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188 Organophosphorus Chemistry

of an excess of triethylamine52 has led to the establishment of an Elcb mechanism similar to that previously proposed for the reaction of (66) with tricyanovinylbenzene. A further account of the electrophilic substitu- tion of (66) has appeared,53 the preferential substitution at position 2 of the cyclopentadiene ring being rationalized in terms of the greater stability of the Wheland intermediate. Dichlorocarbene also attacks (66) at the 2-position, leading to the aldehyde (67).54

CliO

(68) (69)

Comparisons based on U.V. spectra, basicity, and reactions with aldehydes and with nitrosobenzene have been made among the betaines (68; R = Ph, X = P, As, Sb, Bi, S , Se, or Te) and the pyridinium betaine (69; R = H),56 and among the betaines (68; R = H, X = P or As) and the betaine (69; R = H).56

The 3-phospholenium salt (70) with aromatic aldehydes and potassium t-butoxide in THF gave the trienes (71) in low yield,67 presumably via the intermediate phosphine oxides (72). The unsaturated lactones (74) were

0 I- + 2 ArCHO - Ar(CH:CH),Ar

I L \ Mc Me

0 : P / \

Me Me

(72)

52 C. W. Rigby, E. Lord, M. P. Naan, and C. D. Hall, J. Chem. SOC. (B) , 1971, 1192. 63 D. Lloyd and M. I. C. Singer, Chem. and Ind., 1971, 786. 54 Z. Yoshida, S. Yoneda, and T. Yato, Tetrahedron Letters, 1971, 2973. 55 B. H. Freeman, D. Lloyd, and M. I. C. Singer, Tetrahedron, 1972, 28, 343. 56 D. Lloyd and M. I. C. Singer, Tetrahedron, 1972, 28, 3 5 3 . 67 D. Lednicer, J . Org. Chem., 1971, 36, 3473.

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Ylides and Related Compounds 189

PhjP' Br-

(73) (74) 24 . ? I " , ,

OM' K = JJ-NO,-C,H,~, p-Me.C,H,, or Me

obtained 5 8 as single isomers of unknown geometry from the ylide (73) and aldehydes in refluxing dichloroniethane; (73) is stable for several days at - 15 "C.

The phosphonium salt (75) with benzaldehyde and potassium t-butoxide gave the diene (77), as shown in Scheme 3.59 The base alone resulted in

Ph,kH,C(:CH,)CO,Et Br- 2 Ph,,kH:CMe.C(OH)Me2 Br-

Ph,P, PhCH:CH.C(:CH,)C (OH)Mc, 5 ( 7 7 ) (76) 80':::

Reagents: i, MeLi; ii, KOBut; iii, KOBut, PhCHO Scheme 3

the formation of the stable quinquecovalent phosphorane (76), which did not react with benzal deh yde. Trip henylp hosp hine and diphenylc yclopr o- penone gave the stable keten-phosphorane (7QSo With methanol, (78) gave methyl a-phenylcinnamate and the phosphine, while a-phenylcinnamic acid led to the anhydride (Scheme 4). The iminocyclobutenone (79) was formed from (78) and 2,6-dimethylphenyl isocyanide.

2-Aminopyridine adds to the /3-acylvinylphosphonium salt (80) to give the salt (81a) or (81b), which has been used successfully in olefin synthesis.s1 The salts (82) with benzaldehyde and ethanolic ethoxide gave 62 the olefins (83), which were isolated when R1 and R2 were phenyl, but otherwise gave the isomers (85) and/or the adduct (84) by reacting with a further molecule of aldehyde.

58 J. E. T. Corrie, Tetrahedron Letters, 1971, 4873. 59 C. F. Garbers, J. S. Malherbe, and D. F. Schneider, Tetrahedron Letters, 1972, 1421. 6o A. Hamada and T. Takizawa, Tetrahedron Letters, 1972, 1849.

E. Zbiral and E. Hugl, Tetrahedron Letters, 1972, 439. 62 E. E. Schweizer and C. S. Khim, J. Org. Chem., 1971, 26,4033.

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190 0 rganop h osp h or us Ch enzis t r y

pl’yph + Ph,P i Ph,P:CPh.CPh:C:O 0 (78) 92‘:/,

J 1’11, , P 11 (PhCH:CPh-CO),O + Ph,P ,C=C + Ph,P

H ‘CO,Mc Reagents: i, CBHB, R.T.; ii, PhCH:CPh*C02H; iii, MeOH

Scheme 4

(78) + c $ t c Me

hl e

01’ +

Among other interesting phosphoranes used successfully in olefin synthesis are (86),63 (87),64 (88; X = Br, OMe, OPh, SPh, or CN),65 both geometrical isomers of (89),66 (90),67 (91),68 and (92).69

63 B. P. 1250601 (Chem. Abs., 1972,74,4013). 64 M. I. Shevchuk, M. V. Khalaturnik, and A. V. Dombrovskii, J. Gen. Chem. (U.S.S.R.),

1971, 41, 2172. 65 M. Le Corre, Compt. rend., 1971, 273, C , 81. OG R. K. Howe, J . Amer. Chem. SOC., 1971, 93, 3457. 67 M. B. Groen, H. Schadenberg, and H. Wynberg, J. Org. Chem., 1971,36,2797. 6n S . Yoshina and I . Maeba, Chern. and Pharm Bull. (Japan), 1971, 19, 1465. 69 S. Hunig and H.-C. Steinmetzer, Tetrahedron Letters, 1972, 643.

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Ylides and Related Compounds 191

Ph R'

(84)

Ylides have been implicated in the formation of acylcyclopropanes from the y-acyloxyphosphonium salts (93) as and in the very rapid reaction of the tributylphosphine-carbon disulphide adduct (94) with

Ph,P:CHCH,NMe, Ph,P : CR. CO-CO-Ar

(86) (87)

c1

CH: PPh, P h , P : C H a x

CI

CH: PPh,

7 o E. E. Schweizer and W. S. Creasy, J . Org. Chein., 1971, 36, 2379.

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I92 Organophosphorus Chemistry t l3LlfOH> R3C&Rl

Ph3PCH2CH2CR1R2 .0C0.R3 Br- + Ph3P0 I I R 2

42-59';;: (93)

0

? I

I I I I I

I

, I

K + x l ) = C F I A r + Bu,PO Bu,PCS,- + RCER + ArCHO +

R (94)

(95)

(96)

electrophilic acetylenes and aromatic aldehydes to give the benzylidene- 1,3-dithioles (95).71 The speed of the latter reaction was ascribed to the anti-aromatic nature of the postulated intermediate ylide (96), if planar.

3 Selected Applications of Ylides in Synthesis

Natural Products.-A number of 'one-s tep' olefin syntheses have appeared in which phosphine, alkyl halide, and carbonyl compound are allowed to react together in the presence of a suitable epoxide as the source of base. Among them are the synthesis of ( &)-mitorubrin 72 and of the polyene (97) (Scheme 5).73

Sirenin (98) has been obtained via an electrocyclic reaction of a cis-divinylcyclopropane as shown in Scheme 6.74 The trans-olefin synthesis

71 H. D. Hartzler, J. Amer. Chem. Soc., 1971, 93, 4961. 72 R. Chong, R. W. Gray, R. R. King, and W. B Whalley, J. Chenz. SOC. ( C ) , 1971, 3571. 73 G.P. 2 132 032 (Chem. Abs., 1972, 76, 99 874). 7 4 L. Jaenicke, T. Akintobi, and D. G. Muller, Angew. Chem. Internat. Edn., 1971, 10,

492; A. Ah, D. Sarantakis, and B. Weinstein, Chem. Comm., 1971, 940.

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Ylides and Related Compounds

, CHZCH, + Ph,P:CH*CiC.Et 11

193

1 6:;" H * C C - E t

. CH:CH, I l i

+ CICH,CMe:CH.CO,Et + Ph:,P

Ji

0 / \

Reagents: i , MeCH,CH-CH,, 90 "C, 24 h

Scheme 5

J 6 1 1 i , ci C.Et

i

\ I (98)

Reagents: i , PhJ':CH.CH:CHEt; ii, H2, Lindlar catalyst

Scheme 6

i, PhLi i i , MeOlT

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194 Organophosphorus Chemistry

of Schlosser, involving stereospecific protonation of a /3-oxido-ylide, has been applied 75 to the preparation of a sample of ( k )-progesterone pre- cursor (99) containing only 3% of the cis-isomer. Full details have appeared 76 of the synthesis of chlorobiumquinone, and the 1,Sdiene synthesis 77 involving coupling of allylidenephosphoranes with allylic bromides has been applied to the synthesis of squalene.

The dione (100) reacted exclusively at the exocyclic carbonyl in a synthesis 79 of methyl 9 4 s - (101) and 9-trans-trisporates B. Although (+)-dihydro-/3-santalol (103) was obtained from (102) in 90% yield if the hydroxy-group was protected as the borate ester, use of unprotected (102) gave predominantly the isomeric olefin (104)?O Similarly the hydroxy- ketone (105) gave the olefin (106), but similar rearrangements did not occur using the isopropylidene- or ethoxycarbonylmethylene-phosphoranes.

0

‘OH ( 103)

l..

( 103) ‘OH

( 104)

i 5 W. S . Johnson, M. B. Gravestock, and B. E. McCarry, J . Amer. Chem. SOC., 1971, 93, 4332.

76 C. D. Snyder, W. E. Bondinell, and H. Rapoport, J. Org. Chem., 1971, 36, 3951. 77 E. H. Axelrod, G. M. Milne, and E. E. van Tamelen, J . Amer. Chern. SOC., 1970, 92,

2139. 78 U. T. Bhalerao and H. Rapoport, J. Amer. Chem. Suc., 1971, 93, 5311. 79 S. Isoe, Y. Hayase, and T. Sakan, Tetrahedron Letters, 1971, 3691.

W. I. Fanta and W. F. Erman, J. Org. Chem., 1972, 37, 1624.

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Ylides and Related Compounds

n 195

n

Among many other syntheses involving extensive use of ylides are those of lycoxanthin,81 P,y- and y,y-carotene,82 10,ll: lo’, 1 1’-bisdehydrorhodo- an thin,^, ethyl ( - )-ab~cisate,~~ p r ~ p y l u r e , ~ ~ and of juvenile hormone.86 In the course of the last mentioned, the phosphonium salts (107; X = H or Si Me,) were used successfully in olefin synthesis, but reactions involving the salt (107; X = CH,OH) were not successful.

Among hindered ketones reported to give poor yields on methylenation are (108) and (109).s8

+ PhBPCH,CH, CH,Ci C X I‘

( 107)

[2-3H]Lachnophyllum methyl ester has been obtained using the phos- phorane Ph3P: C3H*C02Me, while the phosphorane Ph,P: 14CH- C02Me has been used in the synthesis of 14C-labelled abscisic acid.

Macrocyclic Compounds.-Further information has appeared 91 on the oxidation of bifunctional y1ides:with oxygen to give macrocyclic polyolefins. The bisphosphorane (1 10) with the dialdehyde (1 11) gave the cyclohepta- triene (112), from which the cation (113) was obtained on treatment with

H. Kj~sen and S. Liaaen-Jensen, Acta Chem. Scand., 1971, 25, 1500. 82 A. G. Andrewes and S. Liaaen-Jensen, Acta Chem. Scand., 1971, 25, 1922.

U.S.P. 3 624 105 (Chem. Abs., 1972,76, 72 678). 84 T. Oritani and K. Yamashita, Tetrahedron Letters, 1972, 2521. 86 A. I. Meyers and E. W. Collington, Tetrahedron, 1971, 27, 5979. 8* J. S. Cochrane and J. R. Hanson, J. C. S. Perkin I, 1972, 361. 87 E. Piers, W. de Waal, and R. W. Britton, J . Amer. Chem. SOC., 1971, 93, 5113. 88 A. Deljac, W. D. MacKay, C. S. J. Pan, K. J. Wiesner, and K. Wiesner, Canad. J. Chem.,

1972, 50, 726. 88 F. Bohlmann and T. Burkhardt, Chem. Ber., 1972,105, 521; G. C. Barley, A. C. Day,

U. Graf, E. R. H. Jones, I. O’Neill, R. Tachikawa, V. Thaller, and R. A. Vere Hodge, J . Chem. SOC., (C), 1971, 3308. J. C. Bonnafous and M. Mousseron-Canet, Bull. SOC. chim. France, 1971, 4551. H. J. Bestmann and H. Pfuller, Angew. Chem. Internat. Edn., 1972, 11, 508.

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196 Organophosphorus Chemistry

(1 12)

( 1 13)

trityl f luor~bora te .~~ Among other cyclic polyolefins prepared by Wittig olefin syntheses are the [20]annulene (1 14),93 the dianthr[ 14lannulene (1 1 5),94 and (1 16) 95 (of unknown geometry).

In the first assignment of absolute configuration to a h e l i ~ e n e , ~ ~ the bisphosphonium periodate (1 18), obtained from the binaphthyl (1 17) of known absolute configuration, reacted with base to give ( +)-(P)-penta- helicene (1 19). Wittig reactions have also been used to obtain the stilbenes required for photochemical cyclization to give [8]heli~ene,~~ and a [Glhelicene of known absolute config~ration.~~

+

( 1 14)

92 P. J. Garrett and K. P. C. Vollhardt, Chem. Comm., 1971, 1143. 93 H. Saikachi, H. Ogawa, and K. Sato, Chem. and Pharm. Bull. (Japan), 1971, 19, 97. 94 S . Akiyama and M. Wakagawa, Bull. Chem. SOC. Japan, 1971, 44, 3158. 95 C. D. Tulloch and W. Kemp, Chem. Comm., 1971, 747. 86 H. J. Bestmann and W. Both, Angew. Chem. Internat.Edn., 1972, 11, 296. g7 R. H. Martin and J. P. Cosyn, Synthetic Comm., 1971, 1, 257. s8 J. Tribout, R. H. Martin, M. Doyle, and H. Wynberg, Tetrahedron Letters, 1972,2839.

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Ylides and Related Compounds 197

+ PhLi

2Br-

P h3 P CH, CH2PPh3 -+ +

(115 ) 21%

x c H 2 f p h 3 + 0 CH2PPh3 OHC \ CHO

(116) 127;

-50 "C LiOEt I

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198 Organophosphorus Chemistry

Evidence from their n.m.r. spectra suggests that they exist in the syn-form (121). The bright red thienocyclobutadiene (122) was obtained loo as shown. Among other heteroannulenes synthesized using Wittig olefin syntheses are a thia[l l]annulene,lol an 0xa[l3]annulene,~~~ the oxat1 Slannulene

The bridged hetero[l llannulenes (120) have been obtained as

Ph,6CH2 / LiOMe X 2Br- DMFI

QCHO - CHO + Ph3PCH2 + /

x = s, zo::, x = 0, 2”/,

P 11 Pli,,P: C H P I1

\ - 7 8 C s - /

P ti P h (122) 3.59,’,

t Ph, I’C H.,

\ - X

P t i .,I’ C H + /

LiOEt,

D M F 2Br- -

90 ‘ C

I:: 0 /

x = 0, 15.3O,, X = CH,, 11.2”{,

( 1 23)

99 E. Vogel, R. Feldmann, H. Duwel, H.-D. Cremer, and H. Gunther, Angew. Chem. Internat. Edn., 1972, 11, 217.

loo P. J. Garratt and K. P. C. Vollhardt, J. Amer. Chem. SOC., 1972, 94, 1022. lol A. B. Holmes and F. Sondheimer, Chem. Comm., 1971, 1434. lo2 A. P. Bindra, J. A. Elix, and M. V. Sargent, Austral. J. Chem., 1971, 24, 1721.

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YIides and Related Compounds 199

(123 ; X = 0) which is antiaromatic,lo3 and thia-[17]- and -[21]-annulenes.lo4 With trityl fluoroborate, (123; X = CH,) gave the aromatic cation (124).

The 1,6-dithia[lO]annulene (1 26) lo5 shows no paramagnetic ring-current and is probably non-planar. The synthesis failed with the salt (1 25 ; X = 0).

(126) 4 -6;;

Carbohydrates.-The synthesis of branched-chain sugars containing the gem-hydroxyformyl group has been achieved lo6 by the sequence:

\ H + \ KMnO, -.. / * I 4 ,C:O + Ph,P:CHCN ---+ ,C:CHCN

/C'CHO

The formyl group is attached to the more hindered face of the ring. Among other phosphoranes used in olefin syntheses with protected aldehydo- or keto-sugars are Ph,P: CH- SMe,lo7 Ph3P: CH- C02R,lo8 and Ph,P: CH*P(: O)(OPh)2.10g

4 Selected Applications of Phosphonate Carbanions

Although the magnesium salt (127; M = 4Mg) could be alkylated and acylated on carbon, the potassium salt (127; M = K) in ether-dioxan with chlorotrimethylsilane gave acetonitrile and the phosphate (1 28) as the only identifiable products from a reaction which may involve silylation of the ambident phosphonate carbanion on oxygen.11o Allylic phosphonate

lo3 H. Ogawa, M. Kubo, and H. Saikachi, Tetrahedron Letters, 1971, 4859. lo4 T. M. Cresp and M. V. Sargent, Chem. Comm., 1971, 1458. lo6 P. J. Garratt, A. B. Holmes, F. Sondheimer and K. P. C. Vollhardt, Chem. Comm.,

1971,947. lo6 J. M. J. Tronchet, R. Graf, and R. Gurny, Helu. Chim. Acta, 1972, 55, 613. lo' J. M. J. Tronchet and R. Graf, Helu. Chim. Acta, 1972, 55, 1141. lo8 Yu. A. Zhdanov and L. A. Uzlova, J. Gen. Chem. (U.S.S.R.), 1971, 41, 1401. loS H. Paulsen, W. Bartsch, and J. Thiem, Chem. Ber., 1971, 104, 2545.

M. Kirilov and G. Petrov, Chem. Ber., 1971, 104, 3073.

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200 Organophosphorus Chemistry

Me,CHCH: C(CN)P(:O)P(OEt), + p-O,N -C,H,.CHO

I ( 1 29) NnH

PhCMe:C(CN)P(:O)(OEt), + PhC€IO

NaH ( 130)

PhCH:CH.CPh :C(CN)P(:O)(OEt),

52"o

carbanions react with aldehydes, attack being at either the a- or the y-carbon, depending upon the substituents.lll Thus the anion from (129) reacted entirely at the a-position whereas that from (130) was attacked at the y-position. The phosphonate (1 3 1) with benzaldehyde and sodium hydrogen carbonate gave ll1 the olefins (1 32) and the isomeric phosphates (1 34), formed via the intermediates (1 33).

PhCH(CN)*CH(CN)P(:O)(OEt), + PhCHO

ROH NaHCO,, I Ph C H 0 P ( : 0) (0 E t ) , PhC(CN)CH,CN

PhCH(CN)-C(CN):CHPh + I

(132) ( 1 34)

PhCH-6) 7 I QWOEt),

PhC -CH I I

C N CN

( 133)

Whether a Michael or a Horner reaction occurs when an @-unsaturated ketone is treated with a phosphonate carbanion depends upon the conditions.l12 Chalcone and the ester phosphonate (135) gave the product of a Horner reaction with sodium hydride in diglyme, but Michael addition occurred with sodamide in ether.

The formation of deoxybenzoin on hydrolysis of the product obtained from benzonitrile and the benzylic phosphonate carbanion has been ll1 D. Danion and R. CarriC, Tetrahedron Letters, 1971, 3219. 112 E. D. Bergmann and A. Solomonovici, Tetrahedron, 1971, 27, 2675.

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Ylides and Related Compounds 201

PhCH:CH-CPh: CH.CO,Et 52:,;

PhCH:CH.CO.Ph + (Et0)2P(:O)CH2C02Et

( E t 0) , P( : 0) C H(C0, E t ) C H P h . C H,CO *P h 42%

rationalized as shown in Scheme 7.113 The ratio of the isomeric unsaturated nitriles (136) and (137) obtained from the nitrile phosphorane and 3,3-dimethylcyclohexanone varies from 28 : 72, using methyl-lithium in benzene, to 60 : 40 when one uses sodium hydride in DMF or DMS0.114

PhCN + (EtO),P(:O)CHPh --+

1 1 2 0 PhCH,CO.Ph 4

72%

Scheme 7

0 II

(E to), P- C H P h I

N=CPh

0 (Et0)Zi /I i H P h

N - A P h

The same phosphonate with the anhydride (1 38) gave 115 the phosphonate (1 39 ; X = CN), existing as the acid (1 39) in the solid and as an equilibrium between (1 39) and the lactone (140) in solution. The corresponding product from the ester phosphonate is the lactone (140; X = C02Et) both in the solid and in solution.

113 F. Mathey and J.-P. Lampin, Tetrahedron Letters, 1972, 1949. 114 J. H. Babler and T. R. Mortell, Tetrahedron Letters, 1972, 669. n5 C. Gadreau and A. Foucaud, Compt. rend., 1972, 274, C, 810.

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202

(MeOCH,), (141) R = Pr’ or CSH,,

X i“

60 ‘c

Ph .C - C H, 7 \

,C, ,C’ ‘P(OEt), 0’ 0 I I1

o,H...o

Among interesting olefin syntheses with ester phosphonates are those with the allenic aldehydes (141) 116 and with the steroidal epoxy-aldehyde (142).l17 The yield of allenic carboxylic esters has been increased118 to

RC H : C : C H . C H 0 + ( M eO), P ( : 0) C H,C 0 2 M e

RCH: C:CH- CH:CH.CO,Me

CHO

(EtO),P(:O)CH,CO,Me

C H: CH - CO, hlc

92%

70430% by carrying out the reactions between ketens and ester phos- phonate at 1 15 “C. The phosphonate (MeO),P(: 0)- 14CH,C0, Me has been used in a synthesis of labelled juvenile horrnone.ll9

116 P. D. Landor, S. R. Landor, and S. Mukasa, Chem. Comm., 1971, 1638. 11’ U. Stache, K. Radscheit, W. Fritsch, W. Haede, H. Kohl, and H. Ruschig, Annalen,

1971,750, 149. 11* G. Kresze, W. Runge, and E. Ruch, Annalen, 1972,756, 112. ll9 W. Hafferl, R. Zurflueh, and L. Dunham, J. Labelled Compounds, 1971,7, 331.

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Ylides and Related Compounds 203

5 Ylide Aspects of Iminophosphoranes

The bis(iminophosph0ranes) (143) and (144) have been obtained as shown.120 Electrophilic olefins and the phosphino-imines (145) gave 121

the cyclic iminophosphoranes (146).

CCI, + + R',P(CH,),,PR', + R2NH2 - R2NH.PR',. (CH2);PR',*NHR2 2CI-

K N Hz, 1 R2N:PR1,.(CH2),-PR12:NR2

( 143)

CCI, + + R3P + H,N(CH2'),NH2 --+ R,PNH(CH2),NHPR, 2CI-

K N H ,

R,P: N(CH,),N:PR,

( 144)

R1,PN : CR2,

( 1 45)

Additional examples

+ CH,:CHR3 => R12PQR12

R3

(146)

have been obtained122 of the change in the rate-determining step, from betaine formation to betaine decomposition, in the reactions of aromatic aldehydes with the iminophosphoranes

R22$(N:PR13)2 RZ2,PF6,- + Me3SiF

(148)

R1,P:NSiMe3 R1 = Me, Pr', or Ph

(14') kF4 R2P(N:PR1,), R2PF,- + Me,SiF

( 149) 120 R. Appel, B. Blaser, R. Kleinstuck, and K.-D. Ziehn, Chem. Ber., 1971, 104, 1847. 121 A. Schmidpeter and W. Zeiss, Angew. Chem. Internat. Edn., 1971, 10, 396. lZ2 S . C. K. Wong and A. W. Johnson, J. Org. Chem., 1972, 37, 1850.

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204 Organophosphorus Chemistry

Ph,P: N- C6H4- X as X changes from electron-withdrawing to electron- supplying. d,-p, Bonding between phosphorus and nitrogen in the phosphorane Ph3P:NSO2*CGH4* Me-p is suggested 123 on the basis of its crystal structure.

The trimethylsilyliminophosphoranes (147) with tri- and tetra-fluoro- phosphoranes give the salts (148) and (149), respe~tive1y.l~~

lZ3 A. F. Cameron, N. J. Hair, and D. G. Morris, Chem. Comm., 1971, 918. lZ4 W. Stadelmann, 0. Stelzer, and R. Schmutzler, Z. anorg. Chem., 1971, 385, 142.

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