1981 1577 Reaction of Epoxides with Triphenylphosphine-Thiocyanogen (TPPT) : Preparation of a-Thiocyanatovinyl Ketones, vic-Dithiocyanates, and vic-Dit hiocyanatohyd r ins By Yasumitsu Tamura," Tomomi Kawasaki, Hitoshi Yasuda, Noriko Gohda, and Yasuyuki Kita, Faculty of Pharmaceutical Sciences, Osaka University, 133-1, Yamada-kami, Suita, Osaka, Japan A number of epoxides smoothly react with TPPT under mild conditions to give a-thiocyanatovinyl ketones, vic-dithiocyanates, or vic-thiocyanatohydrins, depending on the structures of the epoxides used. The reactions proceed site- and stereo-specifically, to give a-thiocyanatovinyl ketones from aP-epoxyketones, fhreo-dithio- cyanate from trans-epoxide, eryfhro-dithiocyanate from cis-epoxide, and vic-thiocyanatohydrins from 1,l -di- substituted or fused epoxides, respectively.A possible mechanism for these reactions is put forward. IN a preceding communication,l we showed that the ring-opening thiocyanation of aP-epoxyketones (1)using the combined reagent triphenylphosphine-thiocyanogen (TPPT) was a useful method for the synthesis of a-thiocyanatovinyl ketones (2). We have now found that the treatment of various epoxides [(4) and (6)] with TPPT causes a novel ring-opening reaction to give vic-dithiocyanates (5) or vic-thiocyanatohydrins (7) depend-ing on the structures of the epoxides used. This paper describes these interesting reactions of epoxides with TPPT, the stereochemistry of the products, and the reaction mechanism, including a full account of the work mentioned in the previous communication.l TPPT -Me RESULTS Treatment of the aP-epoxyketones (la-f) with TPPT in dry methylene chloride under argon at -40 "C for several hours gave good yields of the a-thiocyanatovinyl ketones (2a-f).An alternative preparation of (2) by the reaction of (1) with KSCN or NH,SCN was examined, since a-substituted +unsaturated ketones are generally prepared by the reaction of (1) with the corresponding nucleophilic substrate^.^ This route, however, is not a good one for the synthesis of (2). For example, the reaction of KSCN with 2,3-epoxy-3,5,5-trimethylcyclohexanone(lc) in methanol- water gave a 5304 yield of bis-(2,4,4-trimethyl-6-0~0-cyclohex- l-enyl) sulphide (3),instead of the a-thiocyanato- vinyl ketone (Zc), and that of NH,SCN gave a low yield of (2c) together with several unidentified products.The im- portance of (2) as a synthetic intermediate has already been demonstrated briefly in the previous communication.' In the case of monosubstituted or lr2-disubstituted epoxides (4a-d), the reaction proceeds through a site-specific thiocyanation followed by substitution with the SCN- anion to give the corresponding vic-dithiocyanates Ncs+R' NCS~R*k3 (5) (5a-d) in moderate yields (runs 14). As can be seen in the Table, stereospecific formation of threo-(5b) from trans-(4b) and erythro-(5c) from cis-(4c) was observed. Guy et al. have prepared a mixture of (5b) and (5c) by the addition of thiocyanogen to l-phenylprop-l-ene, and assigned their stereochemistry without separation of the isomers, con-sidering the lH n.m.r.data of the related compounds. The n.m.r. data of both (5b)and (5c) are in good accordance with 1578 J.C.S. Perkin I TABLE Results of thiocyanation reactions with TPPT Starting Yield * M.p. ("C) (solvent) Lit. m.p. hnax./Cm-l 6 (in CDC1,) (J/Hz)Run compound Product (%) [b.p. ("C) (mmHg)] or b.p. ("C) (CHC1,) 1 SCN 50 101 .&102.5 101-102 4 2 170 7.5-7.1 (5 H, m, aromatic) ;(CeHe-ether) J 9, 10, H-1; 3.78 (1 H, dd, Ph/9 PhhCN J 9, 10, H-2); 3.62 (1H, dd, (4a) (5a) J 10, 14, H-2) 2 21 63. ti-64.5 2 160 7.40 (5 H, s, aromatic); Me Ncs)+scN Me (n-hexane) 4.57 (1H, d, J 9, H-2) ; 4.1-PhPha 3.6 (1H, m, H-1); 1.53 (3 H, (4b) (5b) d, J 6.7, Me) 3 32 103-104 2 160 7.40 (5 H, s, aromatic); 4.41 (n-hexane-pentane) (1H, d, J 9.5, H-2) ; 4.1-3.6PhA NcsKMe Phs (1 H, m, H-1); 1.88 (3 H, d, A.NCswxN J 6.6, Me)(4C) (54 4 34 2 170 7.6-6.9 (10H, m, aromatic) ; Ph Ph Ph Ph 4.95 (2 H, s, H-1 and H-2) (4d 1 (5d) 5 42 847-90 3 420; 8.6-8.2 (1 H, br s, OH) ; 2 150 7.34 (5 H, s, aromatic); 4.60Ph"*$ Me Ph SCN (2 H, S, H-2); 1.81 (3 H, S, (60) Me)6 69 Oil 3 450; 7.45-7.1 (4 H, m, aromatic) ; 2 160 4.8-4.45 (2 H, m, H-2 anda:" H-3); 3.8-3.3 (1H, br s,OH) ; 3.34 (1H, dd, J 6.4,(6b) (7b) 7 0 a.: 16.6, H21); 2.85 (1 H, dd, J 3.8, 16.6, H-1) 43 [113-118 148-162(7) 3 570; 3.8-3.4 (1 H, m, H-1); 3.1 (0.Wl 2 140 -2.6 (2 H, m, H-2 and OH) ; (6cI (74 2.5-1.1 (8 H, m, H-3, H-6)* Chromatographed or distilled yields are given.the values reported by Guy et aZ.5 The stereochemistry of with TPPT under the same conditions as mentioned for the (5) closely resembles that of vic-dihalides obtained by the reaction of (1) or (4) with TPPT, gave trans-vic-thiocyan- reaction of epoxides and triphenylphosphine dihalides.6 atohydrins (7a-c) (runs 5-7) without formation of the We next examined the reaction of the 1,l-disubstituted vic-dithiocyanates (5). The structure of the thiocyanato- and fused epoxides (6a-c). Treatment of these epoxides hydrin obtained from (6a) was tentatively assigned as (7a) Me OH Me OCOPh PhCOCL (1) NaSCN -CsHsN Ph (2) PhCOCl Ph BrPhr\,,, -hScN C5"E.N [not as (7a')l on the basis of the spectral evidence, and finally confirmed by the direct comparison of the benzoate (8a) with an authentic specimen prepared alternatively from the known bromohydrin (9) as shown.' The SCN- anion of TPPT attacks the less hindered site of (6a) to give the anti-Markownikoff product (7a), in marked contrast with the behaviour in the reaction of (6a) and thiocyanic acid, which affords the Markownikoff product (7a') .* The introduction of the thiocyanato-group to the benzyl position of (6b) was confirmed by the comparison of the n.m.r. data of (7b) with those of its benzoate (8b).Thus the absorption of H, to the hydroxy-group shifted to lower field (from 6 4.8-4.45 to 5.87-5.7) on benzoylation, and appears as a multiplet due to vicinal coupling with Hb and H,, and Hb of the thiocyanato-group (shifting from 6 4.8-4.45 to 4.88 on benzoylation) appears as a doublet due to the vicinal coupling with Ha. If the benzoate had the isomeric structure (8b'), the a-proton of the hydroxy-group would appear as a doublet and that of the thiocyanato-group as a multiplet. DISCUSSION For the mechanism of the above reactions it is sug- gested that the epoxide oxygen combines with the electrophilic phosphorus atom of TPPT to give an intermediate (A) , which undergoes a nucleophilic ring- opening reaction by thiocyanato-anion to give the (3-thiocyanatoalkoxyphosphonium salt intermediate (B) by analogy with the mechanism proposed in the reaction of epoxide with trimethylsilyl trifluoromethanesulphonate or halogenodimethylsulphonium halide in the presence of the base.A similar phosphonium salt intermediate (B) has already been proposed in the reaction of TPPT with some nucleophiles, e.g. alcohols,1° carboxylic acids,ll and organomethallic compounds.12 ,/ SCN OH (i) (ii) H H NCS+R' NCS&R' The intermediate (B) derived from a@-epoxyketones (1) undergoes a facile a-proton abstraction adjacent to the carbonyl group with the SCN-anion followed by a spontaneous elimination of Ph,P=O to give the a-thio- cyanatovinyl ketones (2) (i). The site-specific attack of 1579 the SCN-anion on the a-site of (A) is explained by the stabilisation of the adjacent carbonyl group. Thus, the orbitals composed of the SCN-anion, the epoxide oxygen as the leaving group, and the a-carbon, overlap with the x-bond of the carbonyl as shown in (ii).The intermediate (B), obtained by the site-specific attack of the SCN-anion on the less hindered site of the inter- mediate (A), derived from monosubstituted or 1,2-disubstituted epoxides (4), causes nucleophilic substi- tution of the SCN-anion on the carbon adjacent to the +oxygen atom of the -0-PPh, group with the elimination of Ph,P=O (Arbzov-type reaction lo9l1J3), giving vic-dithiocyanates (5)(iii). When the substitution of SCN-anion is retarded by steric hindrance, as observed in the intermediate (B) derived from 1,l-disubstituted or fused epoxides (6), the hydrolysed product (7) of the P-0 bond is produced (iv).The SN2mechanism is proposed for the formation of (B) from (A) by consideration of the above results, since both the a-site attack of nucleophiles on the ap-epoxyketones and a less-hindered-site attack of the nucleophiles on the epoxides l4are well documented in the SN~ring-opening reactions of epoxides. EXPERIMENTAL 1.r. absorption spectra were recorded on a Shimazu-IR- 27G spectrophotometer, and n.m.r. spectra on a Hitachi R-20A spectrometer. Chemical shifts are reported in p.p.m. (6) relative to SiMe,. Mass spectra were obtained with a Hitachi RMU-6M instrument with a direct-inlet system operating at 70 eV. Column chromatography was carried out on Merck silica gel 60. General ProGedures for the Preparation of ap-Epoxyketones (la-f) .-The following procedure is typical. To a stirred solution of the ap-unsaturated ketone (10 mmol) in methanol (50 ml) containing 30% aqueous H,O, (1.2 equiv.) at -10 to 0 OC, sodium hydroxide (6~,4 ml) was added dropwise and the reaction mixture was monitored by t.1.c.Stirring was continued at the same temperature until the starting material was consumed (several hours) ; in some cases the temperature was allowed to rise to 20 "C. The mixture was then poured into cold water and extracted with CHCl, (2 x 10 ml). The combined extracts were washed with brine, dried over MgSO,, and concentrated under reduced pressure to give the residue, which was distilled or recrys- tallised from an adequate solvent to give the aP-epoxyke- tones (la-f).2,3-EPoxy~yclohexanone(la) .-This was prepared from cyclohex-2-enone, b.p. 78-80 "C at 10 mmHg (lit., 75-78 "Cat 10 mmHg l6 and 76-78 "C at 15 mmHg la). 2,3-E~oxy-3-methylcyclohexanone(lb) .-This was pre-pared from 3-methylcyclohex-2-enone,b.p. 71-73 "Cat 9 mmHg (lit., 86 OC at 16 mmHg17 and 80-82 OC at 12.4 mmHg 16). 2,3-E?~oxy-3,6,6-trimethylcyclohexanone(lc).-This was prepared from 3,6,6-trimethylcyclohex-2-enone,b.p. 76-80 "C at 8 mmHg (lit. ,70-73 "C at 6 mmHg 1s and 80-84 "C at 10 mmHg 20). 2,3-Epoxycyclopentanone (Id) .-This was prepared from cyclopent-2-enone, b.p. 71 "C at 17 mmHg (lit.,*l b.p. is not reported). 4,B-EPoxy-17P-a~etoxyandrostan-3-om (le).-This was prepared from 17P-acetoxyandrost-4-en-3-one,m.p. 132-133 "C (from methanol), m/e 345 (M+).Although this product may have been a mixture of cis-(le) and trans-(le) from a comparison of the reported m.p.s [lit.,22 cis-(le), 169.5-171.5 "C and trans-(le), 160.5-161.5 "C], it was used for the next reaction without separation of the isomers. 3,4-Epoxypentan-2-one (If) .-This was prepared from pent-3-en-2-one, b.p. 36-37 "C at 10 mniHg; villa... (CHCI,) 1 700 cm-l; m/e 100 (M'). Genral Procedures for the Preparation of Epoxides (4a-d) and (6a-c) .-The following two procedures [methods (A) and (B)]are typical. (A)The olefin (10 mmol) was added to a stirred and ice-cooled solution of 85% m-chloroper-benzoic acid (12 mmol) in CH,Cl, (50 ml) . The mixture was allowed to stand at room temperature for 4 h.The solution was washed with 5% NaOH (20 ml) and saturated aqueous NaCl (30 ml), dried over MgSO,, and concentrated under reduced pressure to give the corresponding epoxide. (R)7923 A suspension of olefin (10 mmol), N-bromosuc- cinimide (NBS) ( 10 mmol) , and water (30 ml) ( in some cases, ' dioxan or dimethyl sulphoxide was added) was stirred vigorously at room temperature until the solid NBS dis- appeared (ca. 30 min). The corresponding bromohydrin layer was separated and the aqueous layer was extracted with CHCI,. The combined extract was concentrated under reduced pressure to give the crude bromohydrin, which was treated with potassium hydroxide (13~, 1.5ml). Extraction with ether, concentration, and distillation under reduced pressure gave the corresponding epoxide.1,2-E@oxy-l-phenyZethane (4a) .-This compound is com- mercially available, b.p. 88 "C at 15 mmHg. trans-l,2-E~oxy-l-~henyZ~ro~ane(4b) .-This was pre-pared by a modification of the Guss method [method (B)],7 b.p.95-100 "C at 30 mmHg (lit.,2482 "C at 10 mmHg). cis-1,2-Epoxy-l-phenylpropane(4c) .-This was prepared by a modification of the Kano method [method (B)],,*and also prepared by another method,2s b.p. 80-82 "C at 10 mmHg (lit.,26 80 "C at 10 mmHg). trans-1,2-Epoxy-1,2-diphenylethane(4d) .-This was pre-pared by method (A), m.p. 69-70 "C (from n-hexane) (lit.,2s 69 "C). 1,2-Epoxy-2-phenylPropane(6a) .-This was prepared by a modification of the Guss method [method b.p. 40-45 "C at 0.1 mmHg (lit.,27 62 "C at 2.3 mmHg).1,2-EPoxyindane (6b) .-This was prepared by a modifi-cation of the Guss method [method (B)],7b.p. 150 "C at 13 mmHg (bath temperature) (lit. 105-108 "C at 8 mmHg 28 and 66-67 "C at 25 mmHg ,*). lI2-EpoxycycZolzexune (6c) .-This compound is commer- cially available, b.p. 132 "C. Reaction of 2,3-Epoxy-3,5,5-tvi~~zethylcyclohexanone(lc) with KSCN.-A solution of (lc) (2 mmol) and KSCN (3 mmol) in MeOH-H,O (1 : 1, 2 ml) was allowed to stand at room temperature for 1 day. After removal of the solvent under reduced pressure, the residue was purified by column chromatography on silica gel using chloroform as a solvent to give the sulphide (3) (163 mg, 53%). Recrystallisation from ether-light petroleum gave an analytical sample, m.p.90-91 "C (Found: C, 70.4; H, 8.55. Calc. for C,,H,,O,S: C, 70.55; H, 8.55%); vlnax, (CHCI,) 1 665 and 1 590 cm-l; 6 (CDC1,) 2.35 (4 H, s, C-4 or C-6), 2.31 (6 H, s, 3-Me), 2.23 J.C.S. Perkin I CH,Cl, (6 ml) was added dropwise to a stirred solution of freshly prepared TPPT (ca. 1.2 mmol) in dry CH,Cl, (10 ml) at -40 "C under argon. The mixture was stirred for the requisite period (ca. 3-4 h) under the same conditions, allowed to warm slowly to room temperature, stirred overnight, and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using chloroform as eluant to give the vinyl thiocyanate (2), vie-dithiocyanate (5), or vic-thiocyanatohydrin (7) depending on the epoxide used.The yields, ix., n.m.r. and mass spectral data of the products (2a-f) were given in the previous communication and those of the products (5a-d) and (7a-c) are listed in the Table. 2-ThiocyanatocycZohex-2-enone (2a) .-This was prepared from 2,3-epoxycyclohexenone (la) and TPPT (Found : C, 54.9; H, 4.55; N, 9.3. Calc. for C,H,NOS: C, 54.90; H, 4.61; N, 9.15%). Spectroscopic data of the compounds (2b-f) were fully consistent with the proposed structures, while satisfactory analytical data could not be obtained because of their instability upon recrystallisation or distillation. Com-pounds (5a) and (7c) were identical with the authentic specimen, as determined by comparison of their melting or boiling points and spectral data. threo-l,2-Dithiocyanato-1-phenylpropene (5b) .-This was prepared from trans- 1,2-epoxy- 1-phenylpropane (4b) and TPPT (Found: C, 56.4; H, 4.2; N, 11.85.Calc. for Cl,H1,N,S,: C, 56.40; H, 4.27; N, 11.96%). erythro-1 ,2-Dithiocyanato- 1 -phenylpropane (5c) .-This was prepared from cis-1,2-epoxy-l-phenylpropane(4c) and TPPT (Found: C, 56.3; H, 4.1; N, 11.9. Calc. for C,,H1,- N,S,: C, 56.40; H, 4.27; N, 11.96%). 1,2-Diphenyl- 1,2-dithiocyanatoethane (5d) .-This was pre- pared from irans-1,2-epoxy-1,2-diphenylethane(4d) and TPPT (Found: C, 64.6; H, 4.05; N, 9.45. Calc. for C,,H,,N,S,: C, 64.83; H, 4.08; N, 9.45%). The unknown compounds (7a) and (7b) were confirmed by the conversion into the benzoates (8a)and (8b).Benzoylation of (7a).-A solution of 2-hyroxy-2-phenyl- 1-thiocyanatopropane (7a) (1.5 mmol) in dry CHICl, (6 ml) was added to an ice-cooled solution of benzoyl chloride (1.5 mmol) and triethylamine (1.5 mmol) in dry CH,Cl, (6 ml) . The mixture was allowed to stand at room tempera- ture for 3 h, diluted with CHC1, (30 ml), and washed with dilute HC1, saturated aqueous NaHCO, (10 ml), and satur- ated aqueous NaCl (5 ml). The organic layer was dried over MgSO, and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using CH2C1, as eluant to give the benzoate (8a) (67%). Recrystallisation from methanol gave an analy- tical sample, m.p. 125.5-126 "C (Found: C, 68.45; H, 4.9; N, 4.8.Calc. for C,,H,,NO,S: C, 68.69; H, 5.01; N, 4.71%); v,,~. (CHCI,) 2 150 and 1 695 cm-l; 6 (CDC1,) 7.8-6.9 (10 H, m, aromatic), 4.60 (1 H, d, J 11 Hz, 3-H), 4.50 (1 H, d, J 11 Hz, 3-H), and 2.10 (3 H, s, Me). This compound was identical with a sample prepared by the thiocyanation of the known bromohydrin (9) with NaSCN followed by benzoylation. Benzoylation of (7b).-The benzoate (8b) (73%) was similarly prepared from 2-hydroxy-1-thiocyanatoindane (7b) (1.2 nimol), benzoyl chloride (1.7 mmol), and triethyl- amine (1.5 mmol) in dry CH,Cl, (10 ml). Recrystallisation(4 H, s, C-4 or C-6), and 1.00 (12 H, s, 5-Me2); m/e 306 (&I+). General Procedure for Thiocyanation of Epoxides ( la-f), from CHC1,light petroleum gave an analytical sample, (4a--d), and (6a-c) .-The following procedure is typical.m.p. 50-51 "C (Found: C, 69.1; H, 4.35; N, 4.75. Calc. A solution of the epoxide (l), (4), or (6) (1 mmol) in dry for C,,H,,NO,S: C, 69.12; H, 4.45; N, 4.74%); vnleL (CHCl,) 2 140 and 1 715 cm-l; 6 (CDC1,) 8.5-7.5 (2 H, m, aromatic), 7.7-7.25 (7H, m,aromatic), 5.87-5.7 (1 H, m, 2-H),4.88(1H,d,J2.6H~,3-H),3.73(1H,dd,J7,16.6Hz, l-H), and 3.16 (1 H, dd, J 2.6, 16.6 Hz, 1-H). [0/1209 Received, 31sl July, 19801 REFERENCES Y. Tamura, T. Kawasaki, N. Gohda, and Y. Eta, Tetra-hedron Lett., 1979, 1129. Y. Tamura, M. Adachi, T. Kawasaki, H. Yasuda, and 1’. Kita, J, Chem. SOL, Perkin Trans. 1, 1980, 1132. a Some nucleophiles such as RO-, RS-, R,N-, X-, and CN- have been reported : M.A. Tobias, J. C. Strong, and R. P. Napier,J. Org. Chem., 1970,35, 1709; A. G. Schults, R. D. Lucci, W. Y. Fu, M. H. Berger, J. Erhardt, and W. K. Hagemann, J. Am. Chem. SOC.,1978,100, 2150; L. D.Markley, J. Org. Chem., 1973,38, 3417; A. G.Schultz and D. S. Kashdan, ibid., 1973,38, 3814; M. Tomoeda, M. Inuzuka, T. Furuta, M. Shinozuka, and T. 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