Simple Preparation of Dimeric Cinchona Alkaloid Derivatives on Polystyrene Supports and a Highly Enantioselective Catalytic Heterogeneous Dimerization of Ketenes

A convenient route for the covalent immobilization of quinidine and hydroquinidine pyridazine ethers on insoluble polystyrene supports is described, which avoids the need of chromatographic purifications at any stage. The use of the heterogeneized alkaloid derivatives in the asymmetric organocatalytic dimerization of ketenes afforded high enantioselectivity values (90-97% ee) in the course of 20 reaction cycles.