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Enantiopure Michael addition products of α-cyanoacetates constitute attractive precursors for functionalised quaternary amino acids and other biologically interesting compounds. Since the pioneering work by Ito et al. in 1992 using rhodium(I) in combination with a trans-chelating planar chiral diphosphine, various complementary approaches have been reported; these are critically discussed and compared in this review. The most efficient recent methodologies utilise a bifunctional activation mode; for example, by dinuclear Lewis acid catalysis or by a well-defined hydrogen-bonding network. This strategy can overcome the difficulty that α-cyanoacetates are incapable of two-point binding to a Lewis acid thus hampering the differentiation of prochiral enol(ate) faces.
Peters et al. (Fri,) studied this question.