Cinchona-Derived Chiral Phase-Transfer Catalysts for Other Asymmetric Synthesis

Cinchona-Derived Chiral Phase-Transfer Catalysts for Other Asymmetric Synthesis 

In particular, it is not only the cinchona alkaloids that are suitable chiral sources for asymmetric organocatalysis [6], but also the corresponding ammonium salts. Indeed, the latter are particularly useful for chiral PTCs because (1) both pseudo enantiomers of the starting amines are inexpensive and available commercially (2) various quaternary ammonium salts can be easily prepared by the use of alkyl halides in a single step and (3) the olefin and hydroxyl functions are beneficial for further modification of the catalyst. In this chapter, the details of recent progress on asymmetric phase-transfer catalysis are described, with special focus on cinchona-derived ammonium salts, except for asymmetric alkylation in a-amino acid synthesis. 

The Darzens reaction is a fundamental reaction, the products of which are extremely useful for the synthesis of other molecules. Despite these advantages, the reaction 

Asymmetric Phase Transfer Catalysis. Edited by Keiji Maruoka Copyright 2008 WILEY-VCH GmbH Co. KGaA, Weinheim ISBN 978-3-527-31842-1 

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Several families of efficient chiral phase transfer catalysts are now available for use in asymmetric synthesis. To date, the highest enantiomeric excesses (>95% ee) are obtained using salts derived from cinchona alkaloids with a 9-anthracenylmethyl substituent on the bridgehead nitrogen (e.g. lb, 2b). These catalysts will be used to improve the enantiose-lectivity of existing asymmetric PTC reactions and will be exploited in other anion-mediated processes both in the laboratory and industrially. 

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