Racemic bis(hydroxymethyl)[7]thiaheterohelicene 9 has been prepared in eight steps (33% overall yield) from 2-(hydroxymethyl)benzo[1,2-b:4,3-b′]dithiophene 1. Lipase (Pseudomonas cepacia)-catalyzed transesterification of diol 9 by vinyl acetate in dichloromethane produces optically stable (P)-bis(hydroxymethyl)[7]thiaheterohelicene [(P)-9] with 98% ee along with the corresponding monoacetate [(M)-10] and the diacetate [(M)-11]. Hydrolysis of acetates (M)-10 and (M)-11 by aq. NaOH gives (M)-9 in 77% and 94% ee, respectively. In contrast, the enzymic resolution of diol 9 with Candida antarctica afforded diol (M)-9 in 92% ee. Column chromatography of optically enriched helicenediol 9 on silica gel shows an enantiomeric enhancement. A possible cause of the phenomenon is discussed.
以 2-(羟甲基)苯并[1,2-b:4,3-b′]二
噻吩 1 为原料,通过八个步骤制备了外消旋双(羟甲基)[7]
噻吩 9(总收率 33%)。
二氯甲烷中的
乙酸乙烯酯催化
脂肪酶(头孢假单胞菌)对二元醇 9 进行酯交换反应,生成了光学上稳定的(P)-双(羟甲基)[7]
硫杂
环己烯[(P)-9](ee 值为 98%)以及相应的单
乙酸酯[(M)-10]和二
乙酸酯[(M)-11]。
醋酸酯 (M)-10 和 (M)-11 在 NaOH 溶液中
水解后,(M)-9 的ee值分别为 77% 和 94%。相反,用 antarctica 白色念珠菌酶解二元醇 9 得到二元醇 (M)-9,ee 值为 92%。在
硅胶上对光学富集的螺旋二醇 9 进行柱层析,结果显示对映体增强。本文讨论了造成这种现象的可能原因。