Synthesis of alkyl alpha- and beta-D-glucopyranoside-based chiral crown ethers and their application as enantioselective phase-transfer catalysts

摘要

Chiral monoaza-15-crown-5-type lariat ethers annelated to alkyl 4,6-O-benzylidene-alpha- and beta-d-glucopyranosides have been synthesized. These macrocycles generated significant asymmetric induction as phase-transfer catalysts in a few two-phase reactions. The catalytic effect of the lariat ethers with methoxy, ethoxy, and i-propoxy substituents on C-1 of the sugar unit in both alpha and beta positions was compared. In liquid-liquid two-phase reactions, the nature and position of the substituents did not have much effect. The alpha-anomers were somewhat more efficient in terms of enantioselectivity than the beta forms. In asymmetric Darzens condensations, in the epoxidation of trans-chalcone, in the Michael addition of beta-nitrostyrene and diethyl acetamidomalonate, and in the reaction of 2-benzylidene-1,3-indandione with diethyl bromomalonate, maximum enantioselectivities of 73, 94, 78, and 72%, respectively, were obtained in presence of glucopyranoside-based lariat ethers as catalysts.