Enantioselective Nitrile Anion Cyclization to Substituted Pyrrolidines. A Highly Efficient Synthesis of (3<i>S</i>,4<i>R)</i>-N-<i>tert</i>-Butyl-4-Arylpyrrolidine-3-Carboxylic Acid
作者:John Y. L. Chung、Raymond Cvetovich、Joseph Amato、J. Christopher McWilliams、Robert Reamer、Lisa DiMichele
DOI:10.1021/jo050178+
日期:2005.4.1
practical asymmetric synthesis of N-tert-butyl disubstituted pyrrolidines via a nitrile anion cyclization strategy is described. The five-step chromatography-free synthesis of (3S,4R)-1-tert-butyl-4-(2,4-difluorophenyl)pyrrolidine-3-carboxylic acid (2) from 2-chloro-1-(2,4-difluorophenyl)-ethanone achieved a 71% overall yield. The cyclization substrate was prepared via a catalytic CBS asymmetric reduction
描述了通过腈阴离子环化策略的N-叔丁基二取代的吡咯烷的实际不对称合成。从2氯-1-(2)进行五步无色谱合成(3 S,4 R)-1-叔丁基-4-(2,4-二氟苯基)吡咯烷-3-羧酸(2) 1,4-二氟苯基)-乙酮的总收率达到71%。通过催化CBS不对称还原t-氯胺的丁胺置换,以及受阻仲胺向丙烯腈的共轭加成。关键的腈阴离子5-exo-tet环化伴随C-4中心的完全转化形成吡咯烷环,从而以> 95%的收率和94-99%ee生成1,3,4-三取代的手性吡咯烷。氯代磷酸二乙酯和六甲基二硅叠氮化锂被证明是该环化过程中各自的最佳活化基团和碱。吡咯烷腈的反式-顺式混合物经过动力学控制的差向异构化/皂化作用,得到纯的反式-吡咯烷羧酸目标化合物的化学和光学纯度> 99.9%。该化学也显示适用于电子中性和富取代的苯基底物。