The Catalytic Asymmetric Acetalization

摘要

The Bronsted acid catalyzed acetalization of aldehydes with alcohols is one of the most common transformations in organic synthesis and yet catalytic asymmetric versions, until today, have been entirely unknown [Eq. (1)] .The advent of asymmetric Bronsted acid catalysis has recently enabled the enantioselective generation of chiral N,N-, N,O-, and N,S-acetals, either from imines or directly from aldehydes. The success of these reactions is based on the well-established ability of chiral phosphoric acids to direct the enantioselective addition of nucleophiles to imines. However, the corresponding enantioselective additions to oxocarbenium ion intermediates, which are required for obtaining O,O-acetals, are much less developed. Although acetals are among the most common stereocenters in organic molecules, there are only few examples of their catalytic asymmetric synthesis.