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 β-ketoamides in 28-83 % yield and 79-99 % 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. A series of hydroquinidine derivatives embedded into elastomeric silicone films was prepared and used as insoluble organocatalysts in the asymmetric dimerization of ketenes. A protocol was introduced to compare the productivity/ enantioselectivity of the supported catalysts with those of their analogous soluble counterparts.