WZRing-opening reactions of pyrrolidinylcyclopropenyl cations in alkaline aqueous solution Yoshio Yagyu, Noboru Matsumura, Hirokazu Tanaka, Zyun Maeda and Hiroo Inoue * Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Sakai, Osaka 593, Japan Pyrrolidinylcyclopropenyl cations la,b in alkaline solution at room temperature are converted efficiently into (2)-and (0-a,P-unsaturated amides 3 and 4, respectively, with more electron-donating alkylsulfanyl groups at the P-position. Recently we have reported the synthesis of 1 -tert-butylsulfanyl- 2-methylsulfanyl-3-pyrrolidinylcyclopropenylium perchlorate la and 1 -methylsulfanyl-2-phenyl-3-pyrrolidinylcyclopropenyl-ium perchlorate lb from 2,3-bis(tert-butylsulfanyl)cycloprop-enethione.' Trisubstituted pyrrolidinylcyclopropenyl cations such as la,b are of interest because they may provide useful information about the addition reactions of pyrrolidinylcyclo- propenyl cations with nucleophiles and any resultant ring- opening.The reaction of la,b with hydroxide as a nucleophile has received little attention to date2 and we can now report that the nucleophilic addition of hydroxide to la,b occurs preferentially at the position attached to the pyrrolidinyl group to form the adducts 2a,b. The consequent ring-opening of 2a,b, gives the (2)-and (E)-a,P-unsaturated amides 3 and 4, respec-tively, the stereochemistry of the products being dependent on the nature of the substituents to give the more electron- donating alkylsulfanyl group at the P-position, as shown in Scheme 1.MeS 1 Za, b a R=Bu'S "pb R=Ph MeS 4 Scheme 1 A mixture of la or lb and aqueous NaOH was stirred at room temperature for 1 h, after which chromatography on silica gel with ethyl acetate as eluent gave the ring-opened compounds 3 and 4in 85 and 82 yields, respectively. The IR spectra of 3 and 4 showed a signal due to the C--O stretching of the amide group at 1622 and 1621 cm-', respectively. Furthermore, the 3Cand 'H NMR spectra of 3 and 4 showed a signal for the carbonyl carbon at 6c 165.51 and 168.26 ppm and due to the olefinic proton at 6, 6.82 and 6.85 ppm, respectively. The stereochemistry of the double bond was determined by measuring the NOESY spectra of 5 and 6, which were derived from 3 and 4, respectively, by reaction with lithium aluminium hydride in dry diethyl ether.In the NOESY spectrum of 5, cross peaks were observed between H,(~5~2.36)and Ha(6, 1.39), H, (6, 3.27) and He (~5~2.51) respectively, but not between H, and H, (6, 6.37) and H, and Ha. This result indicates that the methylsulfanyl group is situated close to the pyrrolidinyl and methylene groups and that the methylsulfanyl and tert-butylsulfanyl groups are mutually cis. On the other hand, the NOESY spectrum of 6 showed cross peaks between H, (6,7.37) and H, (6,2.26), Hi (S, 3.39) and Hj (S, 2-50), respectively, but not between H, and H, (S,, 6.20) and Hi and H,, thus indicating that the phenyl group is situated close to the pyrrolidinyl and methylene groups and cis to the methylsulfanyl group.(CH3)3CSAHba 5 The formation of 3 and 4 indicates that the hydroxide nucleophile attacks selectively at the carbon bonded to the pyrrolidinyl group and the resulting pyrrolidinylcyclopropenes 2a,b undergo ring-opening by the cleavage of the (a) and (b) bonds to give 3 and 4, respectively. Recently we proposed that reactions with cyclopropenes can proceed via the formation of vinylcarbenes upon ring-opening.3 On the basis of this mechanism, the conversion of 2a,b into 3 and 4 is thought to proceed via the intermediary formation of vinylcarbenes 7 and 8, respectively, in which the carbenic carbons are stabilized by the more electron-donating alkylsulfanyl groups, followed by the migration of the double bond and protonation, as shown in Scheme 2.8 2a, b 7 Scheme 2 Experimenta1 IR spectra were recorded on a Perkin-Elmer model 1600 FT spectrometer. 'H and 13CNMR spectra were recorded on a JEOL JNM-GX270 FT spectrometer for solutions in CDCl, with tetramethylsilane (TMS) as an internal standard; J values J. Chem. SOC.,Perkin Trans. 1 117 are in Hz. Mass spectra were obtained at 70 eV with a Finnigan mat TSQ 70 or Shimadzu LKB-9000 spectrometer. Elemental analyses were performed with a Yanaco CHN CORDER MT-3 and a Perkin-Elmer 2400 I1 CHNS/O analyser. Column chromatography was performed on silica gel (Wakogel C-300). General procedures for reaction of pyrrolidinylcyclopropenyl cations la,b in alkaline aqueous solution To a suspension of la,b (0.58 mmol) in H,O (10 cm3) was added aqueous sodium hydroxide (10 cm3, 1.74 mmol, 3 equiv.).The turbid solution was stirred at room temperature for 1 h, during which time an oily substance separated out. The mixture was extracted with CH,Cl, (50 cm3 x 2) and the combined extracts were washed with water, dried (Na,SO,) and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel with ethyl acetate as eluent to give 3(85) and 4 (82), respectively. (Z)-3-tert-Butylsulfany1-2-methylsulfanyl-l-(pyrrolidin-1 -yl)- prop-Zen-l-one 3. Pale yellow viscous liquid (Found: C, 55.4; H, 8.0; N, 5.2; S, 24.9. C,,H,,NOS, requires C, 55.55; H, 8.16; N, 5.40; S, 24.72); v,,/cm-' (neat) 2963 2925, 2875, 1622 (M),1551,1414,1367,1339, 1251,1224,1163,1072,789,736 and 703; BH 6.82 (1 H, s, olefin-H), 3.53 (4 H, m, pyrrolidinyl 2',5'-H), 2.24 (3 H, s, SMe), 1.92 (4 H, m, pyrrolidinyl 3',4'-H) and 1.41 (9 H, s, But);amp; 16.71,26.37,26.43, 31.10,44.93,45.86, 48.41, 128.98, 149.56 and 165.51; m/z 259 (M+).(E)-3-Methylsulfanyl-2-phenyl-l-(pyrrolidin-l-yl)prop2-en-l-one 4. Pale yellow viscous liquid (Found: C, 67.85; H, 6.9; General procedure for reduction by LiAIH, To a suspension of lithium aluminium hydride (1.85 mmol) in dry diethyl ether (10 cm3) was added a solution of 3 or 4 (0.37 mmol) in dry diethyl ether (5 cm3) under argon and the mixture was refluxed for 1.5 h. After the mixture was cooled to room temperature, ethyl acetate (25 cm3) and aq.ammonium chloride (25 cm3) were added. The mixture was extracted with diethyl ether (30 cm3 x 2) and the combined extracts were washed with water, dried (Na,SO,) and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel with diethyl ether as eluent to give 5 (68) and 6 (71), respectively. (Z)-1-tevz-Butylsulfanyl-2-methylsulfanyl-3(p prop-l-ene 5. Pale yellow viscous liquid (Found: C, 58.6; H, 9.1; N, 5.9. C,,H,3NS2 requires C, 58.87; H, 9.39; N, 5.71); v,,,/crn-' (neat) 2961 ,2924,2874,2785, 1568, 1471, 1456, 1436, 1392, 1365, 1345, 1319, 1287, 1162, 1123, 877 and 835; 6,6.37 (1 H, s, olefin-H), 3.27 (2 H, s, CH,), 2.51 (4 H, m, pyrrolidinyl 2',5'-H), 2.36 (3 H, s, SMe), 1.78 (4 H, m, pyrrolidinyl 3',4'-H) and 1.39 (9 H, s, Bu'); dc 14.67, 23.64, 31.14, 44.36, 53.66, 61.34, 122.43 and 132.29; m/z 245 (M'). (E)-l-Methylsulfanyl-2-phenyl-3-(pyrrolidin-l-yl)prop-1 -ene 6. Pale yellow viscous liquid (Found: C, 72.2; H, 8.0; N, 5.8. C,,H,,NS requires C, 72.05; H, 8.21; N, 6.00); v,,,/cm-' (neat) 3055,3020,2963,2921,2873,2785,1646,1599,1492,1458, 1441,1373,1346,13 16,1290,1124,1027,878,833,765 and 698; 6,7.37 (5 H, m, phenyl-H), 6.20 (1 H, s, olefin-H), 3.39 (2 H, s, CH,), 2.50 (4 H, m, pyrrolidinyl2',5'-H), 2.26 (3 H, s, SMe) and 1.74 (4 H, m, pyrrolidinyl3',4'-H); dc 17.93,23.48,23.56, 30.34, 54.13, 63.08, 127.08, 127.20, 127.97, 128.11, 135.51 and 139.63. References Paper 5/06402C Received 28th September 1995 Accepted 3 1st October 1995 I18 J. Chem. SOC.,Perkin Trans. I
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