Two-Center Chiral Phase-Transfer Catalysts for Asymmetric Synthesis

Two-Center Chiral Phase-Transfer Catalysts for Asymmetric Synthesis 

Previously, a wide variety of metal-mediated asymmetric two-center catalyses based on a multifunctional catalyst concept was developed [5]. Similar to an enzyme reaction, the synergistic functions of two or more active sites in multimetallic catalysts make substrates more reactive, and control their position in the transition state so that the functional groups are proximal to each other. In order to extend this concept to asymmetric organocatalysis, two ammonium salt moieties were 

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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An all organic catalyst system 38 has been reported by the Maruoka group for directing asymmetric additions of oxindole enolates derived from 36 to nitro-aUcenes 37 under phase-transfer conditions [26] (Scheme 10). The methodology was extended to the synthesis of a tetrahydropyrroloindole scaffold bearing two chiral centers. Asymmetric Michael and Mannich reactions of 3-aryloxindoles directed by chiral phosphonium salt phase-transfer catalysts have been described by the same group [27]. 

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