Methylene-indolines, indolenines et indoleniniums-V(10). Action de reactifs reducteurs 4. Acide formique-formamide sur vincadifformine et tabersonine : Hemisynthese de la vincadine

Claisen rearrangement in indole alkaloid synthesis. Total synthesis of (+-)-tabersonine

“…Attempts at crystallization or sublimation were unsuccessful: ir (CHCls) 3480, 3020, 2830, 2760, 2710, and 1465 cm"1; nmr (CDC13) 5 0.69 (3 N, t, J = 6.5 Hz), 0.95 (2 H, q, J = 6.5 Hz), 1.62 (2 H, m), 2.20-3.80 (10 H, m), 5.29 (1 H, d, J = 10 Hz), 5.80 (1 H, dd, J = 3 and 10 Hz), 7.10 (3 H, m), and 7.50 (2 H, m); uv max (CH3OH) 231 (e 30,750), 287 (6200), and 295 (5700) nm; mass spectrum (70 eV) m/e (rel intensity) (8.4), 79 (17.5). This material was identical on tic analysis (R¡ and 1 % ceric ammonium nitrate-85 % H3P04 color response) with material prepared by the degradation of tabersonine.27, 28 A second product (R¡ value 0.50), 14,15,16,17-dehydroquebrachamine (12a), was crystallized from ethanol-water to give 0.168 g (30.5%) of a white crystalline solid: mp 151-152°; ir (CHC13) 3480, 3020, and 1470 cm"1; nmr (CDC18) S 0.96 (3 H, t, J = 7 Hz), 5.55 (1 H, d, J = 10 Hz), 5.80 (1 H, d, J = 10 Hz), and 6.90-7.30 (7 H, m); uv "" (CH3OH) 226 (e 37,200), 282 (8900), and 291 (6820) nm; mass spectrum (70 eV) m/e (rel intensity) 279 (20.9), 277 (6.6), 253 (7.8), 250 (20.9), 249 (100), 248 (6.9), 247 (4.6), 237 (32), 235 (36), 234 (8.8), 233 (4.3), 221 (4.3), 209 (3.6), 208 (7), 207 (5.9), 206 (5.3), 205 (4.2), 204 (3.9), 183 (3.2), 155 (1.9), 154 (3.6). 143 (1.9), 115 (3.4), 111 (3.9), 110.5 (6.6), 110(3.7), 77(3.6).…”

“…The combined filtrates were evaporated to give 0.550 g of a viscous yellow oil. Chromatography on Florisil (20:1), eluting first with hexane and hexane-benzene to remove impurities, gave upon elution with benzene 0.11 g (19.5%) of one diastereomeric alcohol (3a) as a yellow oil: ir (CHC13) 3475, 3600-3200, 3065, 3015, 2975, 2930, 2815, 2790, and 2740 cm-1; mass spectrum (70 eV) m/e (rel intensity) 296 (100), 280 (7), 279 (6), 278 (9), 277 (5.5), 267 (14.5), 251 (15), 249 (11.5), 237 (15.5), 173 (22.5), 172 (20), 168 (21.5), 167 (19.5) , 158 (25.5), 156 (45), 154 (34), 144 (71), 143 (29), 138 (24), 136 (27.5), 135 (31.5), 130 (45), 124 (30), 123 (32.5), 122 (56.5), 108 (31.5) , 107 (22), 95 (28).…”