Silicone-Supported Cinchona Alkaloid Derivatives as Insoluble Organocatalysts in the Enantioselective Dimerization of Ketenes

A straightforward procedure is presented for the covalentimmobilization of ester and silyl ether derivatives of theCinchona alkaloid 10,11-dihydroquinidine within insoluble cross-linked silicone elastomeric films. These materials were effective heterogeneous organocatalysts in the asymmetric dimerization of ketenes, which provided chiral Weinreb beta-ketoamides in 2883?% yield and 7999?% ee in the course of several recycles. A productivity/enantioselectivity protocol is also proposed to better assess the relative merits of soluble and supported asymmetric catalytic systems towards process intensification.