Regioselective synthesis of hydroxy sulphidesviatrifluoroacetoxysulphenylation of derivatives of allylic alcohols

摘要

J. CHEM. SOC. PERKIN TRANS. I 1988 Regioselective Synthesis of Hydroxy Sulphides via Trif luoroacetoxysulphenylationof Derivatives of Allylic Alcohols Zakaria K. M. Abd El Samii, Mohamed 1. Al Ashmawy, and John M. Mellor" Department of Chemistry, The University, Southampton, SO95NH Reaction of manganese(iii) acetate with diphenyl disulphide in dichloromethane-trifluoroacetic acid in the presence of allylic esters gives trifluoroacetoxy sulphides, which on hydrolysis readily afford vicinal hydroxy sulphides. With acetate esters, neighbouring group participation by the acetate functionality controls the reaction course. Thus regiospecific addition to ally1 acetate affords after hydrolysis only 3-phenylthiopropane-1,2-diol. In contrast, with trifluoroacetate esters the inductive effects of the trifluoroacetate functionality lead to a different regiocontrol.Thus addition of diphenyl disulphide to ally1 trifluoroacetate gives after hydrolysis only 2-phenylthiopropane-1,3-diol. The regio- and stereo- chemistry of addition to a variety of other allylic (and homoallylic) esters is described and the extension of this type of regiocontrol is discussed. In the development of new methods for the functionalisation of trifluoroacetoxysulphenylation of a wide variety of substituted alkenes there is the need to control both regiochemistry and alkenes. In the following papers we describe the reaction with stereochemistry in addition reactions. In those additions unsaturated amides," carboxylic acids," and nitriles.' In this leading to the vicinal addition of a sulphur substituent and an paper we describe the functionalisation of a variety of un-oxygen substituent to an alkene, considerable control has been saturated esters derived from allylic, homoallylic, and other developed.Thus Trost et af.' have used dimethyl(methy1thio)- alcohols. In certain cases these reactions are characterised by a sulphonium tetrafluoroborate as the electrophile and have high degree of regiocontrol, as reported l1 in our preliminary developed regioselective routes to P-hydroxy sulphides. Earlier communication. papers describe the formation of P-hydroxy sulphides via epi-The results of the trifluoroacetoxysulphenylation of the esters sulphonium ion intermediates * generated from arenesulphenyl are shown in the Table.The starting materials were obtained by halide^,^ or from reaction of organic disulphides with either acetylation or trifluoroacetylation of the appropriate alcohol in lead(1v) salts or trifluoroacetic anh~dride.~ All these studies a routine manner. The formation of adducts was in each case have been concerned with the functionalisation of either hydro- achieved by reaction of the unsaturated ester with the appro- carbons or remotely functionalised alkenes. We have extended priate disulphide in dichloromethane-trifluoroacetic acid in the method of Trost et af.based on the use of lead(1v) salts to the presence of manganese(rr1) acetate dihydrate. Work-up permit trifluoroacetoxysulphenylation 697 and hence the syn- afforded in each case crude trifluoroacetate adducts (vmaX.1790 thesis of hydroxy sulphides. In particular, as described else- cm-'), which were then hydrolysed either under mild conditions we find that manganese(rr1) salts can be used with in the case of the adducts of initial unsaturated trifluoroacetates advantage.This modification has permitted us to study the (to afford diols) and of the adducts of some initial unsaturated Table. Hydroxysulphenylation of allylic esters Alkene Disulphide Product(s) Yield ()" CH,=CHCH,OAc (3) (1) PhSCH,CH(OH)CH,OAc (17) 71 CH,=CHCH,O,CCF, (4) (1) HOCH,CH(SPh)CH,OH (24)PhSCH,CH(OAc)CH,OH (30) 11 98 CH,=CHCH,OAc (3)b (2) PrSCH,CH(OH)CH,OH (19) 64 HOCH,CH(SPr)CH,OH (25) 13 CH,=CHCH,O,CCF, (4) CH,=CHCHMeOAc (5)' CH2=CHCHMe0,CCF, (6)d CH,CH=CHCH,O,CCF, (8) CH,=CEtCH,OAc (9) CH,=CHCHPhO,CCF, (7)' (2) (1) (1) (1) (1) (1) HOCH,CH(SPr)CH,OH (25) PhSCH,CH(OH)CHMeOH (20) and (21) HOCH,CH(SPh)CHMeOH (26) and (27) CH,CH(OH)CH(SPh)CH,OH (26) and (27) PhSCH,CEt(OH)CH,OAc (22) HOCH,CH(SPh)CHPhOH (28) 84 65 98 76 99 79 CH,=CEtCH,O,CCF, Me,C=CHCH,O,CCF, (10) (11) (1) (1) HOCH,CEt(SPh)CH,OH (29) PhSCH,CEt(OH)CH,OH (23) PhSCH,CH(OH)CMe,OH (31) 9 90 60 CH,=CHCH,,OAc (13) (1) PhSCH,CH(OH)CH,,OAc (32) 69 CH,=CHCH,,O,CCF, (14) (1) PhSCH,CH(OAc)CH,,OHPhSCH,CH(OH)CH,,OH (33)(34) 5 40 CH,=CHCH,,O,CCF, (16) CH,=CHCH,,OAc (15) (1) (1) HOCH,CH(SPh)(CH,,OH PhSCH,CH(OH)CH,,OH PhSCH,CH(OH)CH,,OAc (35) (37) (36) 45 77 78 a Yields are based on products isolated after chromatographic separation.Products separated after hydrolysis of intermediate monoacetates. 'Inseparable mixture of diols characterised as acetals (see text). Separable mixture of diols characterised as acetals (see text). One diastereoisomer obtained (see text). 2510 (l)R=Ph RSSR(2)R=Pr R3 1(3) R=COCH,, R2=R3=RL=R5=H (4)R'=COCF,, R2=R3=RL=R5= H (5) R'=COCH3, R2=Me,R3=R4=R5=H (6) R'=COCF,, R2= Me R3= RL= R5= H (7) R'=COCF, , R2= Ph, R3= RL= R5= H (8) R'=COCF,, R2=R3 RL= H , R5= Me (9) R'=COCH3, R2=RL=R5=H, R3= Et 3(10) R1=COCF3 , R2=RL= R5= H , R = Et (11) R':COCF3, R2=R3= H RL=R5= Me (12) R'= R3= RG=R5=H ,R2=Ph OR OR (131 R = COCH, (15) R= COCH, (1L) R =COCF3 (16) R= COCF, acetates (to afford hydroxyacetates), or under stronger condi- tions in the case of other acetates (to afford diols).In all cases, unless otherwise stated, products were isolated pure (t.1.c. and spectra) by chromatography, and in most cases were further characterised by preparation of the appropriate mono-or bis-4-nitrobenzoate. Addition of diphenyl disulphide (1) to allyl acetate (3) afforded two monoacetates (17) and (30)after work-up. The regiospecificity of the addition and the isolation of the minor product (30) give a clear indication of the origin of the regio- control. Although an episulphonium ion intermediate (38) might be expected to give products of Markovnikov addition (as observed) the isolation of the ester (30)shows a neigh- bouring group participation by the acetate leading to the intermediate ion (39).Collapse of this ion can then lead to both isolated products after work-up. The absence of acetyl migra- tion on work-up was checked and the structure of the minor product (30) was confirmed by hydrolysis to the diol(18), which was also obtained from the major product (17). In marked contrast, addition of diphenyl disulphide to allyl trifluoroacetate (4) afforded a single diol (24) after work-up. The regiospecific anti-Markovnikov nature of the addition is controlled by the powerful electron withdrawal of the tri- fluoroacetyl group. Neighbouring group participation to give an ion analogous to (39) is no longer favoured.Hence the inductive effect of the trifluoroacetoxy group determines the regiocontrol. Additions of dipropyl disulphide (2) to allyl acetate (3) and trifluoroacetate (4) proceeded in a similar manner. After hydrolysis the acetate (3) afforded the diol(l9) by Markovnikov addition as the major product, and the diol (25) by anti- Markovnikov addition as the minor product. The anti-Markovnikov product (25) was the only diol obtained from allyl trifluoroacetate (4). The isolation of a product of anti-Markovnikov addition to allyl acetate complicated the procedure for isolation ofproducts so that it was not possible to observe acetyl migration in this case. The formation of a J. CHEM. SOC. PERKIN TRANS. I 1988 HO OAc OH ( 30) (311 product of anti-Markovnikov addition in the reaction of allyl acetate with dipropyl disulphide (2) contrasts with the absence of such a product from diphenyl disulphide (1).The difference might be attributed to the great nucleophilicity of an alkylthio group relative to an aryl group. Such a factor might diminish the importance of neighbouring group participation. Additions of diphenyl disulphide (1) to 1-methylallyl acetate (5)and trifluoroacetate (6) were characterised by high regio- but poor stereo-control. The mixture of diols (20) and (21) from the acetate (5)could not be separated but was converted into the mixture of acetals (40) and (41), which again was not separated. The diols (26) and (27) could be separated by chromatography, individually characterised and converted into their respective acetals (42) and (43).From the spectra of the mixture of acetals (40) and (41) the major isomer (41) could be recognised by the signals for 4-H at 6 3.74 and 5-H at 3.93; the minor isomer had signals at 6 4.21 for 4-H and 6 4.32 for 5-H. On the basis of literature precedent l2 the chemical shift differences permit structural assignments and hence the conclusion that the diols (20) and (21) were obtained in the ratio 1:3. In the case of the acetals (42) and (43) structures could be assigned readily by observation of the coupling constant J4,5.In the case of the trans- acetal (42) formed from the diol (26) a large coupling (J4,5 11 Hz) was observed, characteristic of a trans-diequatorially substituted dioxolane.In the case of the cis-acetal (43) formed from the diol(27) a small coupling (J4,53 Hz) was observed. The analogous addition of diphenyl disulphide (1) to 1-phenylallyl trifluoroacetate (7) afforded a single diol (28), further characterised as the acetal (44).Again the stereo-chemistry of the acetal(44) could be assigned from the coupling J. CHEM. SOC. PERKIN TRANS. I 1988 OR2 SPh HO(32)R1:COCH3 R2= H (33) Rrsquo;. H , R~=COCH, (35 1 (34) R1=R2= H OH + PhSAOR Phsamp;OAc (361R = COCH, (38) (37)R = H 0x0 PhSd SPh . (42)Rrsquo;= Me I R2=H (43)R1= H R2=Me 1(441 R: Ph R2=HoSPh constant J4,5(11 Hz), indicative of the trans-diequatorially substituted dioxolane. Thus whilst addition to the acetate (5) proceeds with Markovnikov regiospecificity and little stereo- selectivity, addition to the trifluoroacetate (7) proceeds with both anti- Markovni kov regiospecifici t y and stereospecificit y, in contrast to the addition to the trifluoroacetate (6) which proceeds with anti-Markovnikov regiospecificity but little stereoselectivity.The most likely explanation for the high stereocontrol in addition to (7) is kinetic control of the face of attack of the sulphur electrophile on the alkene. Addition of diphenyl disulphide (1) to but-2-enyl trifluoroacetate (8) againproceeds regiospecifically to give after hydrolysis the same diols (26) and (27) as isolated from addition to the ester (6). Thus addition to this ester (8) is also characterised by low stereoselectivity.Addition to the acetate (9) afforded a single acetate product (22), further characterised by hydrolysis to the diol (23). This diol (23) was obtained as the major product from the tri- fluoroacetate (lo), showing that in such a compound the effect of the trifluoroacetate group is insufficient to control the regio- chemistry. However a small amount of the minor diol (29)was found in the product mixture. The attempted addition of diphenyl disulphide (1) to the trifluoroacetate (11)afforded after hydrolysis the diol(31) as the only product. This diol is most probably formed via solvolytic rearrangement under the acidic reaction conditions prior to addition. The effect of separating the ester function from the double bond was examined in a representative homoallylic acetate (13) and trifluoroacetate (14).As expected, Markovnikov addition 2511 to the acetate (13)afforded as the major product the adduct (32),isolated after mild hydrolysis, and characterised as the diol (34).However a minor product was the acetate (33),isolated after mild hydrolysis. The isolation of this minor product shows that in the case of a homoallylic acetate too neighbouring group participation occurs and can control the regiochemistry. In the case of addition to the trifluoroacetate (14)two diols (34)and (35) were obtained in 40 and 45 yield, respectively. The former (34) was identical with the hydrolysis product from the acetate (13).Hence the trifluoroacetate group, even in a homoallylic ester, exerts a powerful regiocontrol, as shown by the formation of the anti-Markovnikov adduct (35)in 45 yield. Further separation of the ester functions from the double bond was examined in addition to the esters (15) and (16). In those systems the influence of the ester group was substantially removed. The acetate (15) gave the Markovnikov product, isolated as the acetate (36)and converted into the diol (37). Similarly, after addition and work-up, the trifluoroacetate ester (16) afforded the same diol (37), indicating an absence of regiocontrol by the ester substituent. Although our major interest in these results relates to the understanding of substituent effects in the control of additions to substituted alkenes, our programme of synthesis of sulphenyl- ated heterocyclic systems8-10 suggested the use of diols in the synthesis of oxygen heterocycles. We found that under Mitsunobu rsquo; conditions the mixture of diols (34) and (35) was converted in 74yield into 3-(pheny1thio)tetrahydrofuran (45). Our observations of neighbouring group participation in additions to both allylic and homoallylic esters are unexcep- tional.In the halogenation of allyl alcohols and allyl esters earlier studies l4 thoroughly document such effects. More recently rsquo; observations of the 1,3-addition of tellurium tetrachloride to allylic esters have implied ester participation, probably via an intermediate similar to the ion (39).Again recent studies16 have established that in addition of halogen derivatives to homoallylic acetates neighbouring group participation controls the nature of the products. Our results with allylic trifluoroacetates show that the large substituent effect controls the regiochemistry of the reaction. Even in the case of the homoallylic ester (13) a strong substituent effect profoundly influences the nature of the products. To our knowledge, our use of trifluoroacetate esters to control regiochemistry in additions to substituted alkenes has no literature precedent. Engman,rdquo; in a related study, investigated the addition of tellurium tetrachloride to allyl trichloroacetate but found that no reaction occurred. As the conversions of allylic alcohols into their trifluoroacetate esters and the later hydrolysis of adducts to alcohol products are generally straightforward, we believe that our specific illustra- tion of the control of regiochemistry by trifluoroacetate esters in the formation of adducts by trifluoroacetoxysulphenylation may have a much wider generality.In particular, such control is to be expected in the use of other electrophiles. Experimental General experimental details have been described earlier.6 Unless otherwise stated lsquo;H and 13C n.m.r. spectra were recorded with a Bruker 360 AM spectrometer and mass spectra were recorded at 70 eV with a Kratos MS 30 spectrometer fitted with a Digispec D5 50s data system. All solid compounds were microanalysed at University College, London.All oils unless otherwise indicated were observed to be homogeneous (t.1.c.). Preparation of Alcohols.-l-Phenylprop-2-en-1-01 (12) was obtained by reaction of vinylmagnesium bromide with benz- aldehyde in tetrahydrofuran and was isolated in 52 yield after work-up and distillation as a colourless liquid, b.p. 107 "C at 16 mmHg. All other alcohols were obtained from commercial sources. Preparation of Trijluoroacetates.-The alcohol (10 mmol) was stirred at 0deg;C in dichloromethane (50 ml) containing trifluoroacetic anhydride (20 mmol) for 7 h. Removal of volatile material by careful distillation under reduced pressure afforded as a residue the trifluoroacetate, which was used directly. Preparation of Acetates.--The alcohol (10 mmol) was stirred at room temperature in pyridine (20 ml) containing acetic anhydride (20 mmol) and 4-dimethylaminopyridine (50 mg) for 10 h.The mixture was poured into water, neutralised with sodium hydrogen carbonate, and extracted with ether (3 x 30 ml). The combined extracts were washed with saturated aqueous copper sulphate (4 x 30 ml) and then with water (3 x 30 ml). The ethereal solution was dried and evaporated under reduced pressure to give the acetate, which was used directly. General Procedure for Trijluoroacetoxysulphenylation of Unsaturated Esters.-The appropriate disulphide (23.7 mmol) was added at 0 "C to a stirred solution of manganese(m) acetate dihydrate (1.48 g, 5.5 mmol) in dichloromethane (50 ml) containing trifluoroacetic acid (5 ml).The unsaturated compound (7.5 mmol) in a little dichloromethane was quickly added and the solution was stirred for 8 h, poured into water (50 ml), and extracted with ether (3 x 50 ml). The organic phase was washed with aqueous potassium hydrogen carbonate (3 x 50 ml) and then water (3 x 50 ml), dried (MgSO,), filtered, and evaporated under reduced pressure to give a crude product. Hydrolysis of TriJuoroacetates.-The crude trifluoroacetate was dissolved in the minimum amount of ether and stirred at room temperature for 18 h with aqueous sodium carbonate (15; 30 ml). The mixture was partitioned between ether and water and the aqueous phase further extracted with ether (2 x 50 ml). The combined organic extracts were washed with water (3 x 50 ml), dried (MgSO,), filtered, and evaporated under reduced pressure.The crude product was purified by column chromatography. Hydrolysis of Acetates.-The acetate was dissolved in methanol (30 ml) containing added sodium hydroxide. The solution was heated under reflux for 30 min and then con-centrated under reduced pressure. The residue was partitioned between ether and water and the aqueous phase further extracted with ether (3 x 50 ml). Work-up as before and purification by column chromatography afforded the alcohol. Addition of Diphenyl Disulphide to Allyl Acetate.-As in the general procedure diphenyl disulphide (0.8 1 g) was oxidised by manganese(II1) acetate dihydrate (1.48 g) in the presence of allyl acetate (0.74 g).Work-up, hydrolysis of the crude product with sodium carbonate, and purification by chromatography afforded as the less polar fraction 2-hydroxy-3-phenylthio-propyl acetate (17) (0.65 g, 71 w.r.t. diphenyl disulphide); v,,,,(CHCl,) 3 475, 1 740, and 1 590 cm-'; 6, 2.01 (3 H, s, CH,), 2.99 (1 H, dd, J 14 and 7 Hz) and 3.07 (1 H, dd, J 14 and 6 Hz) (CH,S), 3.48 (1 H, s, OH), 3.93 (1 H, m, CHOH), 4.09 (1 H, dd, J 11 and 6 Hz) and 4.18 (1 H, dd, J 11 and 4 Hz) (CH,OAc), and 7.15-7.4 (5 H, complex, aromatic); 6, 20.49 (CH,), 37.59 (CH,S), 66.59 (CH,OAc), 68.04 (CHO), 126.43, 128.88, 129.72, and 135.15 (aromatic carbon), and 170.86 (CO); and as the more polar fraction 1 -hydroxymethy/-2-phenylthio-ethyl acetate (30) (100 mg, 11 w.r.t.diphenyl disulphide) J. CHEM. SOC. PERKIN TRANS. I 1988 (Found: M', 226.0694. C, lH1,O,S requires M, 226.0664); v,,,,(CHCI,) 3 480, 1 745, and 1 590 cm-'; 6,2.00 (3 H, s, CH,), 2.85 (1 H, s, OH), 3.18 (2 H, d, J 6 Hz, CH,S), 3.78 (2 H, d, J 5 Hz, CH,O), 5.01 (1 H, m, CHO), and 7.15-7.45 (5 H, complex, aromatic); 6, 20.82 (CH,), 33.90 (CH,S), 62.75 (CH,OH), 73.75 (CH,OAc), 126.48, 128.99, 129.72, and 135.48 (aromatic carbon), and 170.76 (CO). Both the acetates (17) and (30) on hydrolysis with potassium hydroxide in methanol afforded quantitatively 3-phenylthio- propane-1,2-diol(18), m.p. 71 "C (lit.,I7 72-73 "C) (from ether- light petroleum) (Found: C, 58.6; H, 6.5; s, 17.4. Calc. for C,H,,O,S: C, 58.7; H, 6.5; S, 17.4); vmax,(CHC1,) 3 440 and 1 595 cm-'; 6,2.97 (1 H, dd, J 14 and 7 Hz) and 3.04 (1 H, dd, J 14 and 5 Hz) (CH,S), 3.42 (1 H, s, OH), 3.48 (1 H, s, OH), 3.54 (1 H, dd, J 12 and 3 Hz), and 3.71 (1 H, dd, J 12 and 3 Hz) (CH,OH), 3.77 (1 H, m, CHOH), and 7.15-7.5 (5 H, complex, aromatic); 6, 37.87 (CH,S), 65.3 1 (CH,OH), 70.33 (CHOH), and 126.80, 129.21, 130.14, and 132.62 (aromatic).Addition of Diphenyl Disulphide to Allyl TriYuor0acetate.- Diphenyl disulphide (0.8 1 g) was oxidised by manganese(Ir1) acetate dihydrate (1.48 g) in dichloromethane (50 ml) contain- ing trifluoroacetic acid (10 ml) and allyl trifluoroacetate (1.2 g). The mixture was initially maintained at 0deg;C and then was stirred at room temperature for 18 h. The solution was poured into aqueous sodium carbonate and extracted with ether (3 x 50 ml).The organic phase was washed with aqueous sodium carbonate (2 x 50 ml) and then water (3 x 50 ml), dried (MgSO,), filtered, and evaporated under reduced pressure. Hydrolysis of the crude product with sodium carbonate and purification of the product by column chromatography eluant ethyl acetate-light petroleum (1 : l) afforded as a colourless oil 2-phenylthiopropane- 1,3-diol (24) (0.67 g, 98 w.r.t. diphenyl disulphide); v,,,,(CHCl,) 3 440 and 1 595 cm-'; 6, 3.29 (1 H, m, CHS), 3.65 (2 H, br s, OH), 3.78 (4 H, m, CH,), and 7.2-7.45 (5 H, complex, aromatic); 6, 52.91 (CHS), 63.02 (CH,) and 126.61, 127.58, 129.17, and 132.42 (aromatic carbon). The diol (24) was further characterised as the bis-p-nitrobenzoate, m.p.96 "C (from ether) (lit.," 95-96 "C). Addition of Dipropyl Disulphide to Ally1 Acetate.-Dipropyl disulphide (0.8 1 g) was oxidised by manganese(II1) acetate dihydrate (1.48 g) in the presence of allyl acetate (0.74 g). Work-up, hydrolysis of the crude product with sodium hydroxide in methanol, and subsequent purification by chromatography afforded as a colourless oil a mixture of 3-propylthiopropane- 1,2-diol (19) and 2-propylthiopropane- 1,3-diol (25) (479 mg, 77 w.r.t. dipropyl disulphide) in 5 :1 ratio ('H and n.m.r.); v,,,,(neat) 3 400 cm-'; 6H0.99 (3 H, t, J 7 Hz, CH,), 1.62 (2 H, m, CH,), 2.53 (2 H, t, J 7 Hz, CH,S), 2.59 l H (major isomer), dd, J 14 and 8 Hz) and, 2.67 l H (major isomer), dd, J 14 and 5 Hz (CH,S), 2.88 l H (minor isomer), q, J 7 Hz, CHS, and 3.4-3.85 5 H (major isomer), complex, CH,O, CHO, and OH; and 6 H (minor isomer), complex, CH, and OH; 6, 13.33 (CH,), 23.02 (CH, of major isomer), 23.47 (CH, of minor isomer), 33.24 (CH, of minor isomer), 34.71 (CH, of major isomer), 35.74 (CH, of major isomer), 50.15 (CH of minor isomer), 63.19 (CH, of minor isomer), 65.45 (CH, of major isomer), and 70.65 (CH of major isomer).Addition of Dipropyl Disulphide to Ally1 Trijluoroacetate (4).-Dipropyl disulphide (0.55 g) was oxidised by manganese- (III) acetate dihydrate (1.48 g) in the presence of allyl tri- fluoroacetate (1.2 g). Work-up, hydrolysis of the crude product with sodium carbonate, and purification by chromatography afforded as a colourless oil 2-propylthiopropane- 1,3-diol (25) (0.51 g, 84 w.r.t.dipropyl disulphide); v,,,.(neat) 3 400 cm-'; 6, 1.00 (3 H, t, J 7 Hz, CH,), 1.62 (2 H, m, CH,), 2.54 (2 H, t, J. CHEM. soc. PERKIN TRANS. I 1988 J 7 Hz, CH,S), 2.87 (1 H, m, CHS), and 3.7-3.9 (6 H, complex, CH,O and OH); 6, 13.26 (CH,), 23.34 (CH,), 33.12 (CH,S), 49.77 (CHS), and 63.04 (CH,OH). The diol (25) was further characterised as the bis-p-nitrobenzoate, m.p. 100-102 "C (from ethyl acetate-light petroleum) (Found: C, 53.5; H, 4.5; N, 6.2; S, 7.1.C,,H,,N,08S requires C, 53.6; H, 4.5; N, 6.2; S, 7.1). Addition oj' Diphenyl Disulphide to 1-Methylally1 Acetate (5).-Diphenyl disulphide (0.8 1 g) was oxidised by manganese- (111) acetate dihydrate (1.48 g) in the presence of the acetate (5) (0.54 g).Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded as a colourless oil a mixture of erythro-and threo-3-phenylthiobutane- 1,2-diols (20) and (21) (480 mg, 65 w.r.t. diphenyl disulphide) in the ratio 1 :3; v,,,~(CHCI,) 3 445 and 1 595 cm-'; 6, 1.2 (3 H, complex, CH,), 2.95-3.95 (complex), and 7.15--7.4 (5 H, complex, aromatic); 6, 17.67 (CH, of minor isomer), 19.52 (CH, of major isomer), 37.04 (CH, of minor isomer), 38.37 (CH, of major isomer, 69.33 (CH of major isomer), 69.51 (CH of minor isomer), 72.99 (CH of minor isomer), 73.63 (CH of major isomer), and aromatic carbon signals. Addition of Diphenyl Disulphide to 1 -Methylally1 Trijluoro-acetute (6).---Diphenyl disulphide (0.81 g) was oxidised by manganese(lr1) acetate dihydrate (1.48 g) in the presence of the trifluoroacetate (6) (1.3 8). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded (as the less polar fraction) as a colourless oil, threo-2-phenylthiobutane-1,3-diol(27) (469 mg, 64Yo w.r.t. diphenyl disulphide); v,,,.(CHCl,) 3 430 and 1 590 cm-I; 6, 1.38 (3 H, d, J 7 Hz, CH,), 3.16 (1 H, m, CH), 3.41 (2 H, br, OH), 3.82 (1 H, dd, J 17 and 6 Hz), and 3.91 (1 H, m) (CH,OH), 4.02 (1 H, m, CHOH), and 7.2-7.45 (5 H, complex, aromatic);S, 21.36 (CH,), 58.07 (CHS), 63.12 (CH,OH), 69.43 (CHOH), and 127.44, 129.19, 132.16, and 134.45 (aromatic carbon); his-p-nitroben,7oate, m.p.103 "C (from ether-light petroleum) (Found: C, 58.0; H, 4.1; N, 5.4; S, 6.4. C2,H,,N2O8S requires C, 58.1; H, 4.0; N, 5.65; S, 6.45); and (as the more polar fraction) erythro-2-phenylthiobutane-1,3-diol(26) (252 mg, 34"i,, w.r.t. diphenyl disulphide); v,,,,(CHCl,) 3 445 and 1 590 cm-'; 6, 1.36 (3 H, d, J 7 Hz, CH,), 3.18 (1 H, m, CHS), 3.42 (2 H, br. OH), 3.76 (1 H, dd, J 11 and 5 Hz) and 3.87 (1 H, dd, J 1 1 and 7 Hz) (CH,OH), 4.13 (1 H, m, CHOH), and 7.18-7.48 (5 H, complex, aromatic); 6, 20.38 (CH,), 58.92 (CHS), 63.09 (CH,OH), 68.41 (CHOH), and 127.29, 129.16, 131.97, and 134.55 (aromatic carbon); bis-p-nitrohenzoate, m.p. 141 "C (from ethyl acetate-light petroleum) (Found: C, 58.0; H, 4.2: N, 5.5; S, 6.3.C2,H,,N,08S requires C, 58.1; H, 4.0; N, 5.65; S, 6.4S'?/:,). Addition oj Diphenyl Disulphide to 1 -Phenylullyl TriJuoro- acetate (?). --Diphenyl disulphide (0.81 g) was oxidised by manganese(r1I) acetate dihydrate (1.48 g) in the presence of the trifluoroacetate (7) (1.79 8). Work-up, hydrolysis of the crude product with sodium carbonate, and purification by chroma- tography afforded as a colourless oil 1-phenyl-2-phen~dthio-propane-1 ,3401 (28) (0.73 g, 76 w.r.t. diphenyl disulphide); v,,~~(CHC'l,) 3 530 and 1 590 cm-'; 6, 3.36 (2 H, complex, CHS and OH), 3.69 (1 H, dd, J 12 and 6 Hz) and 3.78 (1 H, dd, J 12 and 5 Hz) (CH,O). 3.99 (1 H, br s, OH), 4.83 (1 H, d, J6 Hz, CNOH),and 7.1-7.4 (5 H, complex, aromatic); 6, 57.72 (CHS), 62.60 (CH,OH), 75.68 (CHOH), and 126.41, 127.33, 127.81, 128.28, 129.00, 132.2 1, 134.07, and 141.52 (aromatic carbon); hzs-p-nirr.ohc.n=oate, m.p.154-1 56 "C (from ether-light petro- leum) (Found: C, 62.05; H, 4.1; N. 5.1; S, 5.6. C~9H2,NZO8S requires C, 62.4; H, 3.9; N, 5.0; S, 5.7). 2513 Addition of Diphenyl Disulphide to But-2-enyl Trijluoroacetate (8).-Diphenyl disulphide (0.81 g) was oxidised by manganese- (111) acetate dihydrate (1.48 g) in the presence of the tri- fluoroacetate (8) (1.3 g). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded (as the less polar fraction) as a colourless oil threo-2-phenylthiobutane-1,3-diol (27) (490 mg, 66 w.r.t.diphenyl disulphide), identical with the sample isolated from the trifluoroacetate (6); and (as the more polar fraction) as a colourless oil erythro-2-phenyl thiobu tane- 1,3-diol (26) (240 mg, 33 w.r.t. diphenyl disulphide) identical with the sample isolated from the trifluoroacetate (6). Addition of Diphenyl Disulphide to 2-Ethylallyl Acetate (9)--Diphenyl disulphide (0.81 g) was oxidised by manganese(I1r) acetate dihydrate (1.48 g) in the presence of the acetate (9) (0.95 g). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded as a colourless oil 2-ethyl-2-hydro.xy-3-phenylthio-propyl acetate (22) (745 mg; 79 w.r.t. diphenyl disulphide); v,,,.(CHCI,) 3 465, 1740, and 1 595 cm-*; 6, 0.90 (3 H, t, J7 Hz,CH,), 1.63 (2 H,q,J7 Hz,CH,), 1.95 (3 H,s,COCH,), 2.93 (1 H, s, OH), 3.13 (2 H, m, CH,S), 4.03 (2 H, m, CH,O), and 7.1-7.45 (5 H, complex, aromatic); 6, 7.12 (CH,), 20.39 (CH,CO), 29.07 (CH,), 41.60 (CH,S), 67.61 (CH,O), 73.29 (quaternary C), 126.23, 128.75, 129.79, and 136.52 (aromatic carbon), and 170.43 (CO).The alcohol (22) was further characterised by hydrolysis to the diol(23) and conversion into the bis-p-nitrobenzoate, m.p. 128 "C (from ether) (Found: C, 58.6; H, 4.3; N, 5.4; S, 6.1. C,,H,,N,08S requires C, 58.8; H, 4.3; N, 5.5; S, 6.3). Addition of Diphenyl Disulphide to 2-Ethylall~yl Trijluoro- acetate (lo).-Diphenyl disulphide (0.8 1 g) was oxidised by manganese(ii1) acetate dihydrate (1.48 g) in the presence of the trifluoroacetate (10) (1.33 g).Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded as a mixture 2-ethyl-3-phenyl- thiopropane- 1,2-diol(23) and 2-ethyl-2-phenylthiopropane-1,3-diol (29) (767 mg, 99 yield w.r.t. diphenyl disulphide; ratio (10:1); v,,,.(neat) 3 420 and 1 590 cm-'; 'H and I3C n.m.r. of the major isomer (23) as already listed under the addition of diphenyl disulphide to the acetate (9);for the minor isomer (29) 6, 1.00 (3 H, t, J 7 Hz, CH,), 1.45 (2 H, 9, J 7 Hz. CH,), 3.53 (6 H, complex, CH, and OH), and aromatic signals; 6, 8.55 (CH,), 25.36 (CH,), 59.90 (quaternary C), 65.63 (CH,O), and 126.92, 129.45, 129.82, and 137.61 (aromatic carbon).Addition of Diphenyl Disulphide to 3-Methylbut-2-enyl Tri-Juoroacetate (1I).-Diphenyl disulphide (0.8 1 g) was oxidised by manganese(m) acetate dihydrate (1.48 g) in the presence of the trifluoroacetate (11) (1.32 g). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purifi- cation by chromatography afforded as a colourless oil 3-methyl-1 -phenylthiobutane-2,3-diol (31) (470 mg, 60 w. r.t. diphenyl disulphide); v,,,.(CHCl,) 3 580 and 1 590 cm-': 6, 1.15 (3 H, s, CH,), 1.19 (3 H, s, CH,), 2.85 (1 H, m) and 3.20 (1 H, m) (CH,S),3.14(1H,brs,OH),3.45(1H,m,CHOH),3.67(1H,s, OH), and 7.1-7.4 (5 H, complex, aromatic); 6, 24.40 (CH,), 26.4 (CH,), 37.38 (CH,S), 72.39 (CCH,), and 126.41, 128.94, 129.80, and 135.49 (aromatic carbon); bis-p-nitrobonmute, m.p.162deg;C (from ether) (Found: C, 58.6; H, 4.5; N, 5.4; S, 6.4. C25H,,N,0,S requires C, 58.8; H, 4.3; N, 5.5; S, 6.351/;). Addition of Diphenyl Disulphide to But-3-enyl Acetate (13).-Diphenyl disulphide (0.8 1 g) was oxidised by manganese(n1) acetate dihydrate (1.48 g) in the presence of the acetate (13) (0.84 g). Work-up, hydrolysis of the crude product with sodium 2514 carbonate, and subsequent purification by chromatography afforded as a colourless oil (the less polar fraction) 3-hydroxy- 4-phenylthiobutyl acetate (32) (617 mg, 69 w.r.t. diphenyl disulphide); vmaX,(CCl4) 3 545, 1 745, and 1 590 cm-'; 6, 1.7-2.0 (2 H, m, CH,CHO), 1.99 (3 H, s, CH,), 2.97 (1 H, dd, J 14 and 8 Hz) and 3.07 (1 H, dd, J 14 and 5 Hz) (CH,S), 3.35 (1 H, br s, OH), 3.82 (1 H, m, CHOH), 4.20 (2 H, m, CH,OAc), and 7.1-7.4 (5 H, complex, aromatic); 6, 20.49 (CH,), 34.72 (CH,CHO), 41.34 (CH,S), 61.14 (CH,OAc), 66.71 (CHOH), 128.1 1, 128.71,129.49, and 135.49 (aromatic carbon), and 170.84 (CO).The alcohol (32) was hydrolysed to give l-phenylthio- butane-2,4-diol (34), characterised as the bis-p-nitrobenzoate, m.p. 91 "C (from ether) (Found: C, 57.9; H, 4.0; N, 5.7; S, 6.4. C,,H,,N,O,S requires C, 58.0; H, 4.0; N, 5.6; S, 6.4); and (as the more polar fraction) 3-hydroxy- 1-(phenylthiomethyl)butyl acetate (33) (44 mg, 5 w.r.t. diphenyl disulphide); vmaX.(CCl4) 3 550, 1 750, and 1 590 cm-'; 6, 1.75-2.05 (2 H, m, CH,CO), 2.00 (3 H, s, CH,), 2.25 (1 H, br s, OH), 3.09 (1 H, dd, J 14 and 5 Hz) and 3.17 (1 H, dd, J 14 and 7 Hz) (CH,S), 3.52-3.70 (2 H, m, CH,OH), 5.17 (1 H, m, CHOAc), and 7.15-7.4 (5 H, complex, aromatic).The alcohol (33) was hydrolysed to give l-phenylthiobutane-2,4-diol(34), characterised as already described. Addition of Diphenyl Disulphide to But-3-enyl TriJiuoroacetate (14).-Diphenyl disulphide (0.8 1 g) was oxidised by manganese- (111) acetate dihydrate (1.48 g) in the presence of the trifluoro- acetate (14) (1.2 g). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chroma- tography afforded (as the less polar fraction) as a colourless oil 1-phenylthiobutane-2,4-diol(34) (296 mg, 40 w.r.t.diphenyl disulphide); v,,,.(CHCl,) 3 480 and 1 590 cm-'; 6, 1.65-1.85 (2 H, m, CH,), 2.94 (1 H, dd, J 14 and 8 Hz) and 3.07 (1 H, dd, J 14 and 5 Hz) (CH,S), 3.09 (1 H, br s, OH), 3.56 (1 H, s, OH), 3.7-3.85 (2 H, complex, CH,O), 3.91 (1 H, m, CHO), and 7.15-7.45 (5 H, complex, aromatic); 6, 37.50 (CH,), 41.38 (CH,S), 60.21 (CH,O), 69.01 (CHOH), and 126.23, 128.92, 132.08, and 133.84 (aromatic carbon), further characterised as the bis-p-nitrobenzoate, m.p. 91 "C (from ether) (already described). Further elution (ether) afforded as the more polar fraction (as a colourless oil) 2-phenylthiobutane- 1,4-diol (35) (329 mg, 45 w.r.t. diphenyl disulphide); v,,,,(CHCl,) 3 420 and 1 590 cm-'; 6, 1.8-2.0 (2 H, complex, CH,), 3.08 (2 H, br, OH),3.35(1H,m,CHS),3.62(1 H,dd,Jlland6Hz)and3.68 (1 H, dd, J 11 and 5 Hz) (CH,O), 3.75-3.9 (2 H, complex, CH,OH), and 7.2-7.5 (5 H, complex, aromatic); 6, 34.59 (CH,), 48.28 (CHS), 59.81 (CH,OH), 64.45 (CH,OH), and 126.25, 127.14, 129.48, and 135.70 (aromatic); bis-p-nitro- benzoate, m.p.106 "C (from ether-light petroleum) (Found: C, 58.3; H, 4.0; N, 5.6; S, 6.6. C24H,,N,08S requires C, 58.0; H, 4.0; N, 5.6; S, 6.45). Addition of Diphenyl Disulphide to Pent-4-enyl Acetate (15).--Diphenyl disulphide (0.81 g) was oxidised by manganese(II1) acetate dihydrate (1.48 g) in the presence of the acetate (15) (0.95 8). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded as a colourless oil 4-hydroxy-5-phenylthiopentylacetate (36) (0.73 g, 78 w.r.t.diphenyl disulphide); v,,,,(CHCl,) 3 540, 1 745, and 1 590 cm-'; 6, 1.5-1.85 (4 H, complex, CH,CH,CO), 2.00 (3 H, s, CH,), 2.89 (1 H, m) and 3.08 (1 H, m) (CH,S), 3.08 (1 H, br, OH), 3.68 (1 H, m, CHO), 4.03 (2 H, t, J 7 Hz, CH,O), and 7.15-7.45 (5 H, complex, aromatic); 6, 20.70 (CH,), 24.84 (CH,), 32.41 (CH,), 41.95 (CH,S), 64.22 (CH,O), 69.20 (CHO), 126.38, 128.91, 129.83, and 135.62 (aromatic carbon), and 170.88 (CO); further characterised by hydrolysis to the diol (37) and conversion into the bis-p-nirro- benzoate. m.p. 101 "C (from ether-light petroleum) (Found: J. CHEM. SOC. PERKIN TRANS. I 1988 C, 58.9; H, 4.5; N, 5.4; S, 6.4. C,,H,,H,O,S requires C, 58.8; H, 4.3; N, 5.5; S, 6.3).Addition of Diphenyl Disulphide to Pent-4-enyl Trijiuoro- acetate (16).-Diphenyl disulphide (0.81 g) was oxidised by manganese(rr1) acetate dihydrate (1.48 g) in the presence of the trifluoroacetate (16) (1.3 g). Work-up, hydrolysis of the crude product with sodium carbonate, and subsequent purification by chromatography afforded as a colourless oil l-phenylthio- pentane-2,Sdiol (37) (582 mg, 77 w.r.t. diphenyl disulphide); v,,,.(CHCl,) 3 420 and 1 590 cm-'; 6, 1.48-1.74 (4 H, complex), 2.92 (1 H, dd, J 14 and 8 Hz) and 3.04 (1 H, dd, J 14 and 5 Hz) (CH,S), 3.58 (2 H, m, CH,OH), 3.69 (1 H, m, CHOH), 3.88 (2 H, br s, OH), and 7.1-7.4 (5 H, complex, aromatic); 6, 28.90 and 33.08 (CH,), 41.90 (CH,S), 62.54 (CH,OH), 69.80 (CHOH), and 126.43, 129.02, 129.87, and 135.85 (aromatic carbon); further characterised as the bis-p- nitrobenzoate, m.p.101 "C (from ether-light petroleum) (already described). Preparation of Aceta1s.-The diol (100 mg) was stirred at room temperature for 1 h in 2,2-dimethoxypropane (10 ml) in the presence of Amberlyst 15 ion-exchange resin as catalyst. The mixture was filtered and the filtrate stirred with solid potassium carbonate (0.5 g) for 5 min. Further filtration, evaporation of the filtrate under reduced pressure, and purification of the residue by column chromatography eluant ethyl acetate- light petro- leum (b.p. 4amp;60 "C) afforded the acetal. By this procedure erythro-2-phenylthiobutane-1,3-diol(26) (100 mg) gave as a colourless oil trans-2,2,6-trimethyl-5-phenyl-thio-1,3-dioxolane (42), 6, 1.37 (3 H, d, J 7 Hz, CH,), 1.38 (3 H, s, CH,), 1.39 (3 H, s, CH,), 2.95 (1 H, dt, J 11, 11, and 5 Hz, 5-H), 3.75 (1 H, q, J 12 and 11 Hz, 4ax-H), 3.83 (1 H, m, 6-H), 3.88 (1 H, q, J 12 and 5 Hz, 4eq-H), and 7.15-7.45 (5 H, complex, aromatic); 6, 19.5 (CH,), 20.5 (CH,), 29.9 (CH,), 49.1 (C-5), 64.7 (CH,), 69.5 (C-6), 98.9 (C-2), and aromatic resonances.threo-2-Phenylthiobutane-l,3-diol(27) (100 nig) gave as a colourless oil cis-2,2,6- trimethyl-5-phenylthio- 1,3-diox-olane (43), 6, 1.34 (3 H, d, J 7 Hz, CH,), 1.46 (3 H, S, CH,), 1.49 (3 H, S, CH,), 3.02 (1 H, m, 5-H), 3.97 (1 H, dd, J 12 and 2 Hz, 4-H), 4.22 (1 H, dd, J 12 and 2.5 Hz, 4-H), 4.34 (1 H, m, 6-H), and 7.15-7.45 (5 H, complex, aromatic); 6, 19.57 (CH,), 20.06 (CH,), 28.26 (CH,), 51.26 (C-5), 65.22 (CH,), 67.65 (C-6), 99.19 (C-2), and aromatic resonances. erythro-1-Phenyl-2-phenylthiopropane-1,3-diol(28) (1 50 mg) gave as a colourless oil trans-2,2,6-trimethyl-5-phenylthio-1,3-dioxolane (44), 6, 1.47 (3 H, S, CH,), 1.53 (3 H, s, CH,), 3.28 (1 H, dt, J 11, 11, and 5 Hz, 5-H), 3.93 (1 H, q, J 12 and 11 Hz, 4ax-H), 4.04 (1 H, q, J 12 and 5.5 Hz, 4eq-H), 4.70 (1 H, d, J 1 1 Hz, 6-H), and 7.G7.5 (10 H, complex, aromatic); 6, 19.12 (CH,), 29.50 (CH,), 49.15 (C-5), 64.76 (CH,), 76.41 (C-6), 99.15 (C-2), and aromatic resonances.Acetuls (40) and (41) jronz the 1-Phenylthiobutane-2,3-diols (20) and (21).-By the foregoing procedure the mixture of 1-phenylthiobutane-2,3-diols (20) and (21) gave as a colourless oil a mixture of acetals (40) and (41).The major trans-isomer (41) showed 6, 1.32 (3 H, d, CH,), 1.39 (6 H, s, CH,), 3.06 (1 H, dd, J 13 and 6 Hz) and 3.19 (1 H, dd. J 13 and 6 Hz) (CH,S), 3.74 (1 H, m, 4-H), 3.93 (1 H, m, 5-H), and 7.15--7.45 (5 H, complex, aromatic); 6, 18.36 (CH,), 27.15 (CH,), 27.47 (CH,), 36.41 (CH,), 77.14 (CH), 80.89 (CH), 108.64 (C-2), and aromatic resonances. The minor cis-isomer (40) showed 6, 1.24 (3 H, d, CH,), 1.39 (3 H, s, CH,), 1.46 (3 H, s, CH,), 2.97 (1 H, dd, J 13 and 6.5 Hz) and 3.08 (1 H, dd, J 13 and 6.5 Hz) (CH,S), 4.21 (1 H, m, 4-H), 4.32 (1 H, m, 5-H), and 7.1 5-7.45 (5 H, complex, aromatic); 6, 15.39 (CH,), 25.74 (CH,), 28.46 (CH,), 34.70 (CH,), 73.63 (CH), 77.50 (CH), and aromatic resonances.J. CHEM. SOC. PERKIN TRANS. I 1988 3-Phenylthiotetrahydrofuran (amp;).-To a stirred solution of a mixture of l-phenylthiobutane-2,4-diol(34), 2-phenylthio- butane-lP-diol(35) (0.21 g), and triphenylphosphine (0.26 g) in dry tetrahydrofuran (30 ml), diethyl azodiformate (0.17 g) in tetrahydrofuran (10 ml) was added dropwise under nitrogen at room temperature. After 10 h water (20 ml) was added and the mixture was extracted with ether (3 x 50 ml). The combined organic extracts were dried (MgSO,), filtered, and evaporated under reduced pressure to afford after chromatography eluant ethyl acetate-light petroleum (30: 70) as a colourless oil 3-phenyfthiotetrahydrofuran (45)(140 mg, 74) Found: Mf , 1 80.0606(51).C ,H ,OS requires M, 180.06051; vmax.(CHCl,) 1 590 and 1 485 cm-'; 6, 1.88 (1 H, m) and 2.28 (1 H, m) (CH,CH,O), 3.60 (1 H, dd, J9 and 5.5 Hz) and 4.07 (1 H, dd, J 9 and 6.5 Hz) (CH,O), 3.7-3.95 (3 H, complex, CHS and CH,O), and 7.15-7.4 (5 H, complex, aromatic); 6, 33.26 (CH,CH,O), 44.88 (CHS), 67.53 (CH,O), 73.58 (CH,O), and 126.67, 128.97, 130.66, and 135.70 (aromatic carbon). Acknowledgements We thank the Egyptian Education Bureau for financial support through the Channel Scheme, and Mrs. J. Street for n.m.r. spectra. References B. M. Trost, T. Shibata, and S. J. Martin, J. Am. Chem. Soc., 1982, 104, 3228. 2 W. A. Smit, N. S. Zefirov, I. V. Bodrikov, and M. Z.Krimer, Acc. Chem. Re.,., 1979, 12, 282. 3 Y. Masaki, K. Hashimoto, K. Sakuma, and K. Kaji, J. Chem. SOC., Chem. Commun., 1979, 855; W. Dumont and A. Krief, ibid., p. 673; K. C. Nicolaou, S. P. Seitz, W. J. Sipio, and J. F. Blount, J. Am. Chem. SOC.,1979, 101, 3884. 4 B. M. Trost, M. Ochiai, and P. McDougal, J. Am. Chem. SOC.,1978, 100, 7103. 5 N. Furukawa, T. Morishita, T. Akasaka, and S. Oae, Tetrahedron Lett., 1979, 3973; N. Furukawa, T. Morishita, and S. Oae, Tetrahedron, 1981, 37, 2539. 6 A. Bewick, J. M. Mellor, and W. M. Owton, J. Chem. SOC.,Perkin Trans. 1, 1985, 1039. 7 J. M. Mellor and D. L. Bruzco de Milano, J. Chrm. Soc., Perkin Trans. I, 1986, 1069. 8 Z. K. M. Abd El Samii, M. I. A1 Ashmawy, and J. M. Mellor, Tetrahedron Lett., 1986, 27, 5293. 9 2. K. M. Abd El Samii, M. I. A1 Ashmawy, and J. M. Mellor, J. Chem. SOC., Perkin Trans. 1, 1988, 2523. 10 Z. K. M. Abd El Samii, M. I. A1 Ashmawy, and J. M. Mellor, J.Chem. SOC.,Perkin Trans. 1, 1988, following paper; see also Tetrahedron Lett., 1987, 28, 1949. 11 Z. K. M. Abd El Samii, M. I. A1 Ashmawy, and J. M. Mellor, Tetrahedron Lett., 1986, 27, 5289. 12 F. A. L. Anet, J. Am. Chem. SOC.,1962, 84, 747. 13 0.Mitsunobu, Synthesis, 1981, 1. 14 S. Winstein and L. Goodman, J. Am. Chem. SOC.,1954, 76, 4368, 4373; 1957, 79, 4788; J. H. Nayler, J. Chem. SOC., 1959, 189; M. Tisserand, C. R. Acad. Sci., Ser. C, 1966,263, 1550; 264,531; 265,392. 15 L. Engman, J. Am. Chem. SOC.,1984, 106, 3977. 16 H. Kohn, M. B. Bean, C. von Rohrscheidt, M. R. Willcott, and E. W. Warnhoff, Tetrahedron, 1981, 37, 3195. 17 H. L. Yale, E. J. Pribyl, W. Braker, F. H. Bergeim, an W. A. Lott, J. Am. Chem. SOC.,1950, 72, 3710. 18 M. V. A. Baig and L. N. Owen, J. Chem. SOC.C, 1967, 1400. Received 12th October 1987; Paper 7/1821