Asymmetric reduction of various types of ketones with lithium aluminum hydride partially decomposed with (-)-N-methylephedrine and N-ethylaniline.
作者:NORIHIKO TANNO、SHIRO TERASHIMA
DOI:10.1248/cpb.31.837
日期:——
The asymmetric reduction of open chain enones to the corresponding optically active allylic alcohols was achieved in higher chemical (92-100%) and optical (78-98% e.e.) yields than those for cyclic enones (58-88% chemical and 34-58% optical yields). The observed high optical yields for optically active allylic alcohols can be explained on the assumption that, unlike cyclic enones in which the double bonds are fixed in s-trans conformation, open chain enones can be reduced in their s-cis conformations. An optically active propargylic alcohol was similarly produced from an ynone in 88% chemical and 76% optical yields by means of the present asymmetric reduction. When the same asymmetric reduction was applied to simple aromatic and aliphatic ketones by using 1.8 eq of the chiral reducing agent, the corresponding optically active alcohols were obtained in 88-100% chemical and 51-90% optical yields (for aromatic ketones) and in 78-98% chemical and 0-67% optical yields (for aliphatic ketones). On the basis of the results obtained in this and the preceding paper, a possible structure of the exploited chiral reducing agent is proposed and the transition states for the asymmetric reduction are discussed.
开放链烯酮的不对称还原反应成功将其转化为相应的光学活性烯丙醇,化学产率(92-100%)和光学产率(78-98% e.e.)均高于环状烯酮(化学产率为58-88%,光学产率为34-58%)。相应的光学活性烯丙醇高的光学产率可以解释为,与固定在s-trans构象中的环状烯酮不同,开放链烯酮可以在其s-cis构象中进行还原。通过本不对称还原法,从一种炔酮中也成功获得了光学活性的丙炔醇,化学产率为88%,光学产率为76%。当对简单的芳香酮和脂肪酮应用相同的不对称还原,使用1.8倍当量的手性还原剂时,得到的相应光学活性醇的化学产率为88-100%(芳香酮)和78-98%(脂肪酮),光学产率分别为51-90%(芳香酮)和0-67%(脂肪酮)。基于本研究及前一篇论文中获得的结果,提出了所利用的手性还原剂的可能结构,并讨论了不对称还原的过渡态。