Phosphine Oxides and Related Compounds

BY B. J. WALKER

1 Introduction

The major development of the year is that of phosphine oxide-based olefin synthesis into a really useful method complementing the Wittig reaction.

2 Preparation of Acyclic Phosphine Oxides

Both sulphur trioxide and sulphuryl chloride fluoride oxidize phosphines (and triphenylarsine) to the corresponding oxides in excellent yields under mild c0nditions.l The effect of various iron compounds as catalysts for the oxidation of phosphine to phosphine oxide have been investigated ;2 triphenylphosphine oxide is formed quantitatively at 30-70 "C in oxygen at one atmosphere.

Various heptylbis-(5-substituted-2-thienyl)phosphine oxides (1) have been prepared by Friedel-Crafts reaction of heptylphosphoryl chloride with the

0 II

'\CH Ph 2PCH

\ Me (ii) H ~ O ~ Me OMe OMe

G. A. Olah, B. G. Gupta, A. Garcia-Luna, and S. C. Narang, J. Org. Chem., 1983,48,1760. * I. Ondrejkovicova, V. Vancova, and G. Ondrejovic, Collect. Czech. Chem. Commun., 1983,

48,254.

59

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60 Organophosphorus Chemistry

appropriate th i~pene .~ Reactions of phosphorus anions have been used to synthesize phosphine oxides. Several primary and secondary alkyldiphenyl- phosphine oxides are available from the reaction of diphenylphosphine oxide with the appropriate alkyl halide in the presence of sodium bis-[Zmethoxy- (ethoxy)]aluminium h~dr ide .~ The phosphine oxide (3) has been prepared as a separable mixture of isomers by the reaction of diphenylphosphide with the lactone (2).& The E-isomer was used in the key olefination step in a total synthesis of the macrolide antibiotic milbemycin p3.

A new route to optically active trialkylphosphine oxides, and hence phosphines, has been reported.6 The key step, the conversion of the optically active phos- phinite (4) to phosphine oxide, is extremely sensitive to the solvent mixture used, and even under the most favourable conditions involves considerable racemization. Small levels of optical activity (0-8 % enantiomeric excess) have been induced in the phosphine oxide product by hydrolysis of the phosphonium salt ( 5 ) under phase-transfer conditions using optically active quaternary ammonium salts as chiral catalyst^.^

0 0

99% O.P. 55% O . P .

H2° ( A r C H ) P’ I- - + R1

‘Ph

0 II

/ p \ A r C H 2 4 Ph

R

Another surprisingly stable compound containing a P==P bond has been isolated.* Reaction of the sterically hindered arylphosphonic dichloride (6) with magnesium gives the crystalline diphosphene oxide (7), which, not surpris- ingly, is rapidly hydrolysed by water. The tris(diphenylthiophosphinoy1)meth- anide (8) has been isolated as its tetra-n-butylammonium salt.s

a E. A. Krasil’nikova, A. I. Rasumov, and E. S. Sharafieva, Zh. Obshch. Khim., 1982, 52, 925 (Chem. Abstr., 1982, 97, 11 094). N. Suzuki and M. Yamashita, Shizukoa Daigaku Kogakubu Kenkyu Hokoku, 1981, 32, 95 (Chem. Abstr., 1983, 98, 89 508). A. B. Smith, 111, S. R. Schow, J. D. Bloom, A. S. Thompson, and K. N. Winzenberg, J. Am. Chem. SOC., 1982, 104, 4015. M. Moriyama and W. G. Bentrude, Tetrahedron Lett., 1982, 23, 4547. J. Bourson, T. Goguillon, and S. Juge, Phosphorus Sulfur, 1983, 14, 347. M. Yashifuji, K. Ando, K. Toyota, I. Shima, and N. Inamoto, J. Chem. SOC., Chem. Cornmun., 1983,419. S . 0. Grim, S. A. Sangokoya, I. J. Colquhoun, and W. McFarlane, J. Chem. SOC., Chem. Commun., 1982,930.

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Phosphine Oxides and Related Compounds 61

0 I1 THF ,O OC

ArPC12 + M g _______c

ultrasound

(6) L

0 II

ArP =PAr

(7)

A r =

Bu DBUt Bu

3 Preparation of Cyclic Phosphine Oxides

Quin's group have reported the synthesis of a number of tricyclic phospholene oxides, e.g., (9), by the McCormack reaction.I0 The isomeric bicyclic phosphine

S S II I1

I Ph2P=S LXJ

(8) (9) X = 0, S , CH2, o r N-tosyl

oxides (10) and (11) are formed by a similar reaction of 4-methyl-1-vinylcyclo- hexane with methylphosphonous dichloride, followed by hydrolysis.ll At higher temperatures in hexane a similar reaction provides the rearranged oxides (12) and (13), while prolonged reaction at room temperature gives (14) and (15).

Y Y

(14) X = M e , Y = 0 ( 1 0 ) X = M e , Y = 0 ( 1 2 ) X = M e , Y = 0

(11) X = 0, Y = M e (13) X = 0, Y = M e (15) X = 0 , Y = M e

Similar reactions occur with 4-t-butyl-1 -vinylcyclohexene ; surprisingly, these initially give an adduct with the t-butyl group formally axial, although this slowly isomerizes. The tricyclic phosphine oxide (16) and hence the phosphine (17) have been synthesized by a similar approach (Scheme 1),12 with a view to lo L. D. Quin, M. D. Gordon, and J. E. MacDiarmid, J. Heterucycl. Chem., 1982, 19, 1041.

la L. D. Quin, A. N. Hughes, H. F. Lawson, and A. L. Good, Tetrahedron, 1983,39,410. L. D. Quin and J. E. MacDiarmid, J. Org. Chem., 1982, 47, 3248.

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62 Organophosphorus Chemistry

m- / (J-J=---J=J / /I B r-

Ph B r

ii, iii \

1 x 7 , v

Ph

viii, ix

J

-vi, vii m-) Ph / \ 0

Ph 0

( 1 9 )

I Ph

(18)

Reagents: i, PhPBr,, 25 "C, 10 days; ii, CHCl,, reflux; iii, H 2 0 ; iv, NBS, H 2 0 ; v, DBU, DMSO; vi, KHS04, xylene; vii, HSiC13, py; viii, Bu'Li; ix, H202

Scheme 1

generating the analogue (18) of the lox-pentalenyl di-anion. However, attempts to generate (18) by the reaction of (17) with various bases gave either intractable tars or, in the case of t-butyl-lithium, the phospholene oxide (19) through 1,4-addition of the nucleophile. ( +)-( 1 S,4R)-4-0xo-l -phenyl-2-phospholene 1-oxide (22) has been synthesized from the phospholene oxide (20) by epoxidation and isomerization followed by resolution as (21).13 The absolute configuration of (22) is based on its X-ray structure. 13 R. Bodalski, T. Janecki, Z . Galdecki, and M. Glowka, Phosphorus Sulfur, 1983, 14, 15.

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Phosphine Oxides and Related Compounds 63

Ph 0

0 / \ Ph 0

( 2 0 ) ( 2 1 ) R = o-camphanyl

( 2 2 ) R = H

A new synthesis giving good yields of highly substituted phosphole oxides (24) is the reaction of aluminium halide complexes of cyclobutadienes (23) with phosphonous dichlorides (Scheme 2).14 The synthesis of several substituted dibenzophospholes, e.g., (25), has been reported.16

)+”“l -1i-L - ii li,ii *----

/ \ R O

/ \ ( 2 3 ) R C1

- A 1 C 1 4 ( 2 4 ) 60-80%

Reagents: i, RPCl,; ii, NaOH

Scheme 2

4-t-Butyl-2-methyl-6-alkyl-l,4-oxaphosphorin 4-oxides (27) have been obtained by hydrolysis of the salts (26).16 The oxides (27) undergo acid-catalysed ring- opening and aldol condensation to give 3(2H)-phosphorinone 1-oxides (28)

l4 K. S. Fongers, H. Hogeveen, and R. F. Kingma, Tetrahedron Lett., 1982, 24, 1423. l6 J. Cornforth, R. H. Cornforth, and R. T. Gray, J. Chem. Soc., Perkin Trans. 1, 1982,2289;

J. Cornforth, A. F. Sierakowski, and T. W. Wallace, ibid., p. 2299; J. Cornforth, D. D. Ridley, A. F. Sierakowski,’D. Uguen, and T. W. Wallace, ibid., p. 2317; J. Cornforth, D. D. Ridley, A. F. Sierakowski, D. Uguen, and T. W. Wallace, ibid., p. 2333.

l6 G. Markl, K. Hock, and D. Matthes, Chem. Ber., 1983,116, 445; G. Mgrkl and K. Hock, ibid., p. 1756.

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64 Organophosphorus Chemistry

/=\ t Bu 8

Me C

t/ \\ Bu 0

Reagents: i, 20H-; ii, H 3 0 +

Scheme 3

i - O A c I

EtP-CH

ii, iii

P-E t

A c0 U O A c

d A c

Reagents: i, SMAD; ii, HCI, EtOH; iii, AcOH, py

Scheme 4

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Phosphine Oxides and Related Compounds 65

(Scheme 3), which can be converted into h6-phosphorins. Phosphine oxide analogues (31) of ct- and p-D-glucopyranoses have been prepared through dihydrobis-[2-methoxy(ethoxy)]aluminate reduction of the isomeric cyclic phosphinites (29) followed by acid hydrolysis of the unstable phosphine oxide (30) (Scheme 4).17 The four diastereomers of (31) were separated and their structures established using 400 MHz lH n.m.r. spectroscopic data. The effect of aryl substitution on the synthesis of dihydrophenophosphazines (32) from diarylamines and phosphorus trichloride has been investigated.l* Bis-(o-formylpheny1)phenylphosphine (33) undergoes acid-catalysed hydration

with oxidation-reduction to give the phosphine oxide (34).1° Involvement of a dioxaphosphorane intermediate is suggested. 1,5-Di-p-tolyl-3,7-diphenyl-3,7- dithio-l,5-diaza-3,7-diphosphacyclooctane (36) is formed on treatment of (35) with sulphur.20

H

qCHO ap-ph CHO

H 0 , THF 2

Ph

(33) (34)

R

Ti" Ph P

(35) R

l7 H. Yamamoto, K. Yamamoto, S. Inokawa, M. Yamashita, M. A. Armour, and T. T.

l8 H. S. Freeman, L. D. Freedman, and M. A. Muftah, J. Org. Chem., 1982,47,4637. l@ E. F. Landvatter and T. B. Rauchfuss, J. Chern. SOC., Chem. Commun., 1982, 1170. ao B. A. Arbusov, 0. A. Erastov, G. N. Nikonov, D. S. Yufit, and Yu. T. Struchkov, Dokl.

Nakashima, J. Org. Chem., 1983, 48,435.

Akad. Nauk SSSR, 1982,267,650 (Chem. Abstr., 1983,98, 126 259).

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66

4 Structural and Physical Aspects

Organophosphorus Chemistry

Structures determined by X-ray methods include that of the anion (8),21 and conclusions about the low-energy conformational processes in triphenylphos- phine oxide have been drawn from a study of X-ray data of a large number of four-co-ordinated triphenylphosphorus compounds.22

Both X-ray and n.m.r. spectroscopic evidence indicates a predominant axial orientation of the diphenylphosphinoyl substitutent in the 2-[1,3]- dithianyldiphenylphosphine oxide (37) and this is explained on the basis of an anomeric effect.23 Both 13C and 31P n.m.r. spectroscopy have been used to investigate structures of the phosphole oxide dimer (38)24 and the alkali-metal salts of dioctylphosphine oxide.25

S

PPh \\

I

Me\ P 3 I\

Me

In view of the current interest in highly sterically hindered aryl phosphorus compounds the report of dipole moment studies of trimesityl- and triphenyl- phosphine oxides is worth noting.26 The thermodynamics of hydrogen-bonded complexes of triphenylphosphine oxide2' and various alkylarylphosphine oxides28 with a number of hydroxyl-containing compounds have been studied.

5 Reactions at Phosphorus

The reactions of allenylphosphine oxides leading to five-membered phosphorus heterocycles have been reviewed.29

S. 0. Grim, R. D. Gilardi, and S . A. Sangokoca, Angew. Chem., Int. Ed. Engl., 1983, 22, 254. E. Bye, W. B. Schweizer, and 3. D. Dunitz, J. Am. Chem. SOC., 1982, 104, 5893.

Fredrich, J. Org. Chem., 1982, 47, 5038.

20, 83.

23 E. Juaristi, L. Valle, C. Mora-Uzeta, B. A. Valenzuela, P. Joseph-Nathan, and M. F.

24 L. D. Quin, K. A. Mesch, R. Bodalski, and K. M. Rietrusiewicz, Org. Magn. Reson., 1982,

25 S . Raynal, W. Bergeret, J. C. Gautier, and A. Breque, Tetrahedron Lett., 1983, 24, 1791. 26 A. P. Timosheva, G. V. Romanov, S. G. Vul'fson, A. N. Vereshchagin, T. Ya. Stephanova,

and A. N. Pudovik, Izv. Akad. Nauk SSSR, Ser. Khim., 1982,604 (Chem. Abstr., 1982,97, 55 901).

27 P. Ruostesuo and U. Salminen, J. Chem. Res. ( S ) , 1983, 46. 28 N. I. Dorokhova, A. A. Shvets, L. V. Goncharova, and 0. A. Osipov, Zh. Obshch. Khim.,

1982, 52, 2636 (Chem. Abstr., 1983, 98, 72 280). 29 C. M. Angelov, Phosphorus Sulfur, 1983, 15, 177.

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Phosphine Oxides and Related Compounds 67

The chemical and electrochemical oxidations of triphenylphosphine sulphide and phosphorothioates in acetonitrile have been in~estigated.~~ In both reactions, triphenylphosphine sulphide initially gives a product formulated as a dimeric di-cation (39), but this rapidly decomposes on removal of the solvent or exposure to air. Triphenylphosphine oxide and sulphide form radical anions on treatment with potassium in ether at low temperature or by one-electron reduction at a Hg cathode in DMF.31 The photo-oxidation (sensitized by polymer-supported Rose Bengal) of triphenylphosphine selenide to the oxide has been shown to be highly solvent-dependent. 32

Ex / - ' Ph

1 A r 1 Ar

( 4 0 ) X = 0 (42)

( 4 1 ) X = l o n e p a i r

The oxide (40) is thermally stable to at least 140" C, whereas the parent l-phenyl-3-benzophosphepin (41) decomposes to naphthalene and, presumably, phenylphosphinidene at 80 0C.33

Diary1 secondary phosphine oxides have been used to synthesize biphosphine ligands (42) via a substitution-reduction sequence.34

6 Reactions of the Side-chain

A new synthesis of vinylphosphine oxides is available from the addition of secondary phosphine oxides to enol acetates to give (43), followed by thermolytic

R2

c 250 OC, 8 h e

0 II

I R2

Me2PC =CH R1

( 4 3 )

30 R. L. Blankespoor, M. P. Doyle, D. J. Smith, D. A. Van Dyke, and M. J. Waldyke,

31 W. Kaim, P. Haenel, and H. Bock, Z. Naturforsch., B: Anorg. Chem., Org. Chem, 1982,

32 S . Tamagaki and R. Akatsuka, Bull. Chem. SOC. Jpn., 1982, 55, 3037. 33 G. Mark1 and W. Burger, Tetrahedron Lett., 1983, 24, 2545. 34 R. L. Wife, A. B. Van Oort, J. A. Van Daorn, and P. W. N. M. Van Leeuwen, Synthesis,

J . Org. Chem., 1983, 48, 1176.

37, 1382.

1983, 71.

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68 0 rganop hosp ho rus Chemistry

elimination of acetic The Diels-Alder addition of optically pure (&)- trans-benzylphenyl-[~-(methoxycarbonyl)vinyl]phosphine oxide (44) to l-vinyl- naphthalene is regiospecific to give a 65 : 35 mixture of the diastereomeric phosphine oxides (45) and (46).3s Dieckmann-type cyclization of these oxides provides a convenient synthesis of the 17-phosphasteroid system (Scheme 5).

0

Ph

0

COOMe

( 4 5 )

( 4 4 ) COOMe -4 0

Reagents: i , NaH; ii, HzO

Scheme 5

Ph i "\\ Ph - "YPh

Ph

B r B r

( 4 7 )

Reagents: i, Br,, CCI,, 150 "C; ii, BuLi; iii, CCI,

Scheme 6 35 J. Sander, H. J. Kleiner, and M. Finke, Angew. Ckem., Int. Ed. Engl., 1982,21, 537. 36 R. Bodalski, J. Koszuk, H. Krawczyk, and K. Pietrusiewics, J. Org . Ckem., 1982,47,2291.

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Phosphine Oxides and Related Compounds 69

The or-halogenation of tertiary phosphine oxides has been in~estigated.~' Direct bromination of dibenzylphenylphosphine oxide gave all three possible diastereo- meric or,or'-dibromo-derivatives (47). Alternative halogenation, via formation of the mono- or di-lithiated species followed by reaction with carbon tetrachloride, gave monochlorination products (48) with kinetically controlled diastereomeric ratios.

a(e- 0 0 + mpce 0 OH OH

OH ( 4 9 )

( 5 0 )

Reagents: i , CyNHz; ii, 2 LDA, -50 "C

Scheme 7 In connection with his work on the generation of phosphapentalenyl di-anions,

Quin has investigated the base-catalysed rearrangement of epoxycyclopenta- phosphole oxides (49) and (50) to allylic alcohols (Scheme 7).38 The enamine-type chemistry of (51), prepared from the corresponding ketone, has been investi- gated.39

2-Hydroxyalkylphosphine oxides, generated in various ways, have been used

NaH, DMF

0

c1 clQ

( 5 2 ) ( 5 3 )

37 M. Heuschmann and H. Quast, Chem. Ber., 1982,115, 3384. 38 L. D. Quin and H. F. Lawson, Phosphorus Sulfur, 1983, 15, 195. 38 J. B. Rampal, K. D. Berlin, and N. Satyamurthy, Phosphorus Sulfur, 1982, 13, 179.

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70 Organophosphorus Chemistry

I

D I

A

a Lo B W

+

X 0=a,

d

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Phosphine Oxides and Related Compounds 71

extensively to synthesize alkenes. Base-treatment of (52), obtained from the corresponding epoxide, has been used to prepare the trans-bicyclo[6.1 .O]nonene (53)40 and trans-cyclonona-l,5-diene isomers.41 In the latter case the procedure to the trans,trans-isomer (56) involved stepwise elimination of two moles of phosphinic acid from the diastereomers (54) and (55); however, (56) is presumed to undergo rapid Cope rearrangement since the products isolated are the dienes (57) and (58). The generation and reactions of P-ketoalkylphosphine oxide carbanions (59) have been in~estigated.~~ Surprisingly, these reagents do not form alkenes with aldehydes or ketones, although they can be alkylated with various reagents. The failure of the Horner-Wittig reaction is explained by a combination of an unfavourable equilibrium for the addition to carbonyl and

0

phdJYR1 0 A R 2

( 5 9 )

Reagents: i, R3R4CO; ii, R3X Scheme 8

OL i 0

" SPh i, ii ~ [::yRi ph2pY

(60) iii

(61) Reagents: i, R'Li; ii, RVHO; iii, CF,COOH, H20

40 A. C. Connell and G. H. Whitham, J. Chem. SOC., Perkin Trans. 1, 1983, 989. 41 A. C. Connell and G. H. Whitham, J. Chem. SOC., Perkin Trans. 1 , 1983, 995. 42 R, S. Torr and S. Warren, J. Chem. SOC., Perkin Trans. 1, 1983, 1173.

Scheme 9

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72 0 rganop hosp hor us Chemistry

the relatively low driving force for diphenylphosphinic acid elimination (Scheme 8). A direct route to ketones (61) from 1-(pheny1thio)vinyldiphenylphosphine oxide (60) is provided by nucleophilic alkylation followed by in situ reaction with aldehydes of the anion thus generated (Scheme 9).43 Allylphenyl sulphides, e.g., (62), containing a terminal alkene group are difficult to prepare and readily undergo 1,3-phenylthio shifts to give the non-terminal alkene, e.g., (63). How- ever, it is now reported that (62) can be readily prepared by a method involving Horner-Wittig olefination (Scheme

HO

” 1. - vi Ph2P ;“3

SPh

- vi Ph2P ;“3 SPh

7 0 0 0 H

Reagents: i , BuLi; ii, (,,,I ; iii, CF,COOH; iv, ocl ; v, PhSLi, THF; vi, NaH,

THF; vii, hv

Scheme 10 The stereospecific olefination method involving synthesis, separation, and

base-catalysed decomposition of diastereomeric P-hydroxyalkylphosphine oxides has been used for the preparation of pure isomers of y,a-unsaturated acetals (Scheme 1 l).45 The same principle has been extended to trisubstituted a l k e n e ~ . ~ ~ The yields are generally still good, but the diastereomeric hydroxyphosphine oxides involved are less stable in some cases and the routes to them are less stereoselective. However, the method works reasonably well for the synthesis of (E)- and (2)-allylic amines (Scheme 12).47 Unfortunately, (2-substituted-2-amino)-

45 S. Warren and A. T. Zaslona, Tetrahedron Lett., 1982, 23, 4167. 44 R. S. Torr and S. Warren, J. Chem. SOC., Perkin Trans. I , 1983, 1169. 45 C. A. Cornish and S. Warren, Tetrahedron Lett., 1983, 24, 2603. 46 A. D. Buss and S. Warren, Tetrahedron Lett., 1983, 24, 111. 47 D. Cavalla and S. Warren, Tetrahedron Lett., 1982, 23, 4505.

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Phosphine Oxides and Related Compounds 73

:r 0 =ahl c a

N c a Dow

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74

c\;l a 2

N cr:

3

N el 2

a 2

r( cr:

N p:

y .rl I .d

c*? cr: 2

7 0=e,

N c e,

Organophosphorus Chemistry

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Phosphine Oxides and Related Compounds 75

1 2 ( 6 4 ) R = R = a l k y l ;

1 2 R = H , R = a l k y l

o R' R~ O L i i - Ph 25)( A Ph NHCOPh

L i

p h 2 j 3 2 y i:: R2

1 2 (65 ) R = H , R = a l k y l ; 1 2

R = R = a l k y l p h ' p q N H C O P h

R1 R2

NHCOPh

I Reagents: i, 2BuLi; ii, RCHO; iii, NH4Cl; ivy NaH, DMF CHR

Scheme 13

alkylphosphine oxides (64) do not undergo the Horner-Wittig reaction and the synthetically equivalent amides (65) must be used (Scheme 13).48

Unlike the analogous phosphonates, dialkoxymethyldiphenylphosphine oxides (66), readily obtained from chlorodiphenylphosphine and orthoformates, undergo the Horner-Wittig reaction with aldehydes and ketones and so offer a

0

2 3 i - i v R R C=C(OR1)2

(66) Reagents: i , LDA; ii, R2R3CO; iii, H 2 0 ; iv, KOBU'

Scheme 14

( 6 7 )

convenient new route to the synthetically useful ketene 0,O-acetals (67) (Scheme 14)29 Phosphine oxides such as (68) have been used for olefinations in vitamin D3

la,25-Dihydroxycholecalciferol (71), a physiologically active 4a D. Cavalla and S. Warren, Tetrahedron Lett., 1983, 24, 295. 4g T. A. M. Van Schaik, A. V. Henzen, and A. Van der Gen, Tetrahedron Lett., 1983, 24,

1303. H. T. Toh and W. H. Okamura, J. Org. Chem., 1983, 48, 1414. E. G. Baggiolini, J. A. Iacobelli, B. M. Hennessy, and M. R. Uskokovic, J . Am. Chem. Soc., 1982, 104,2945.

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76 Organophosphorus Chemistry

0

( 6 9 ) R = SiR; THF, -78 'C, Ih \

vitamin Ds metabolite, has been prepared in excellent yield by reaction of the protected ketone (69) with the phosphine oxide carbanion (70).61 The penta-2,4- dienylphosphine oxide (73), prepared from the 1 -oxa-2-phosphacyclohepta-4,6-

M e 0 M e M e

t PhMePCH2C=CCH=CHPh II I I

Ph' *O ( 7 3 )

( 7 2 )

Reagents: i, MeMgI; ii, NaBH,; iii, H S 0 4

Scheme 15

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Phosphine Oxides and Related Compounds 77

diene (72) (Scheme 15) provides a route to conjugated trienes via the Horner- Wittig reaction.sa

A new phosphorus-based olefin synthesis, which to some extent combines the advantages of the Wittig, the phosphonate, and the phosphine oxide methods, is provided by reactions of the a-lithioalkylphosphinothioic amide (74) with aldehydes and ketones, followed by methylation of the P-hydroxy-adducts (75) formed (Scheme 16);53 alkylation of (74) followed by lithiation and the same

S S OH

I I \ R 2 N M e

II i, ii II I d Ph-P-CH2Li - Ph-P-CH C

iii

( 7 5 ) (74)

0 Ph-P-SMe II + CHTCR 1 2 R

I NMe

i, ii -

Reagents: i, RIRZCO; ii, HsO+; iii, Me1

Scheme 16

s

Naph t hy 1

0

Scheme 17

6a C. C. Santini and F. Mathey, Can. J. Chem., 1983,61, 21. 63 C. R. Johnson and R. C. Elliot, J. Am. Chem. Soc., 1982,104,7041.

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78 Organophosphorus Chemistry

sequence of reactions provides routes to 1,Zdisubstituted alkenes. Pure E- and 2-isomers can be obtained in appropriate cases by separation of the diastereomeric P-hydroxy-adducts prior to methylation. The method has been applied to the synthesis of (+)- and (-)-hop ethers (77) by use of the optically active phos- phinothioic amide (76) (Scheme 17),64 although in this case two equivalents of base are required because of the presence of an amino-hydrogen.

7 Phosphine Oxide Complexes and Extractants

A distribution study has been carried out on the extraction of uranium in sea water using solutions of trioctylphosphine oxide in cyclohexane, and the optimum conditions for a quantitative recovery determined.66 The effect of added trioctylphosphine oxide on the distribution of a number of P-diketones between various solvents and aqueous perchlorate solution has been investigated.66

54 C. R. Johnson, R. C. Elliot, and N. A. Meanwell, Tetrahedron Lett., 1982,23, 5005. 55 S. Degetto, M. Faggin, A. Moresco, and L. Baracco, Bull. Chem. SOC. Jpn., 1983, 56, 904. 56 T. Sekine, T. Saitou, and H. Iga, Bull. Chem. SOC. Jpn., 1983,56,700.

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