Synthesis of novel chiral crown ethers derived from D-glucose and their application to an enantioselective Michael reaction

Abstract

New chiral monoaza-15-crown-5 derivatives anellated to methyl 4,6-di-O-butyl-α-D-glucopyranoside have been synthesized from 1 using the 4,6-O-benzylidene protecting group (removed by acetic acid) and 2,3-di-O-benzyl groups (removed by catalytic hydrogenolysis). The alkylation of the hydroxy groups in 1 and 5 with benzyl chloride and bis(2-chloroethyl) ether, respectively, were carried out in two-phase reactions using phase-transfer (PT) catalysts. These sugar-based crown ethers showed significant asymmetric induction as chiral PT catalysts in the Michael addition of 2-nitropropane to chalcone (90% ee). The substituent at the nitrogen atom of the crown ethers has a major influence on both the chemical yield and the enantioselectivity.