Abstract
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.
1 Introduction
2 Rhodium, Iridium and Ruthenium Catalysts
3 Palladium and Platinum Catalysts
4 Aluminium Catalysts
5 Organocatalysis
5.1 Cinchona Alkaloids
5.2 Thiourea-Derived Catalysts
5.3 Cinchona Alkaloid-(Thio)Urea Hybrids
5.4 Iminium Catalysis
6 Phase-Transfer Catalysis
7 Conclusions
Key words
amino acids - asymmetric catalysis - α-cyanoacetate - quaternary stereocentre - Michael addition
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