Reduction of 1-(4-chloro-2-pyridyl)-2-(2-pyridyl)ethanone oxime (3) using zinc in trifluoroacetic acid gave the corresponding racemic pyridylethylamine 4 in excellent yield without reductive removal of the chlorine atom. A subsequent diastereomeric crystallization of the amine 4 with an optically active cis-cyclohexanecarboxylic acid derivative in the presence of a catalytic amount of 3,5-dichlorosalicylaldehyde was found to give the desired R-amine 6 in 42% yield via a ”crystallization-induced asymmetric transformation”.
用
锌在
三氟乙酸中还原 1-(4-
氯-2-
吡啶基)-2-(2-
吡啶基)乙酮
肟 (3),得到相应的外消旋
吡啶乙胺 4,收率极高,且无需还原去除
氯原子。随后,在一定量的
3,5-二氯水杨醛催化下,用光学活性顺式
环己烷羧酸衍
生物对胺 4 进行非对映结晶,发现通过 "结晶诱导不对称转化 "得到了所需的 R-胺 6,产率为 42%。