Asymmetric Michael Addition of Malonates to Enones Catalyzed by an α-d-Glucopyranoside-Based Crown Ether

Abstract

The chiral monoaza-15-crown-5 lariat ether annelated to methyl-4,6-<i>O</i>-benzylidene-α-<sc>d</sc>-glucopyranoside has been applied as a phase-transfer catalyst in several Michael addition reactions under mild conditions affording the adducts with good to excellent enantioselectivities. In the addition of α-substituted diethyl malonates to <i>trans</i>-chalcones, the substituents of the reactants had a significant impact on the yield and enantioselectivity. Among the reactions of substituted diethyl malonates, that of diethyl-2-acetoxymalonate gave the best results (up to 97% ee). New phase-transfer-catalyzed cyclopropanation reactions (MIRC reactions) of a few enones were also developed using diethyl 2-bromomalonate as the nucleophile. The corresponding chiral cyclopropane derivatives were formed with enantioselectivities up to 92% from 2-benzylidenemalononitrile starting materials, in up to 60% enantiomeric excess using 2-benzylidene-1,3-diphenyl-1,3-propanediones, and in up to 88% optical purity applying <i>trans</i>-chalcones as the starting materials.