Enantioselective cyanoformylation of aldehydes organocatalyzed by recyclable cinchonidine ammonium salts

Enantiomerically enriched O-methoxycarbonyl cyanohydrins were obtained using an enantioselective addition of methyl cyanoformate to aldehydes organocatalyzed by a dimeric anthracenyldimethylderived cinchonidine ammonium salt (1 mol % catalyst loading) in the presence of substoichiometric amounts of triethylamine (20 mol %). Aromatic and heteroaromatic aldehydes usually afford high enantioselectivities (up to 96%) and quantitative yields of the corresponding O-methoxycarbonyl cyanohydrins, whereas aliphatic and alpha,beta-unsaturated aldehydes give lower enantioselectivities (up to 60%) in high yields. The observed sense of the enantioselection was always the same, and the organocatalyst was almost quantitatively recovered by ether-promoted precipitation Without any loss of activity. The use of resin-supported cinchonidine-derived ammonium salts as an organocatalyst in this transformation was also explored. (C) 2009 Elsevier Ltd. All rights reserved.