Catalytic Asymmetric Esterification of Ketenes

摘要

Ester formation by addition of alcohols to ketenes was discovered 100 years ago,when Hermann Staudinger prepared diphenylketene as the first isolated member of this versatile and reactive family,and by reaction with ethanol formed the ethyl ester of diphenylacetic acid.As soon as unsymmetrical dis-ubstituted ketenes were prepared it became apparent that esterification of these ketenes by alcohols generates a new chiral center,and by 1919 an attempt was made by Weiss to achieve asymmetric synthesis in this reaction,by the addition of the optically active alcohol (-)-menthol to phenyl(4-tolyl)-ketene (1) [Eq.(1)].