Wall-Coated Polymer Brushes as Support for Chiral Organocatalysts in Microreactors

Cinchona alkaloid and proline derivatives as enantioselective catalysts were covalently attached onto the inner walls of a microreactor using glycidyl methacrylate polymer brushes. The successful formation of the organocatalyst-functionalized brush layers on flat silicon oxide surfaces was confirmed by several techniques such as Fourier transform infrared (FT-IR), ellipsometry, and X-ray photoelectron spectroscopy (XPS). The applicability of the cinchona alkaloid (cinchonidine or quinidine)-and proline-containing polymer brushes in a microreactor was demonstrated for the Diels-Alder reaction between anthrone and N-substituted maleimides, and the aldol reaction between 4-nitrobenzaldehyde and cyclohexanone, respectively, which showed moderate conversions (up to 55% and 23%, respectively) and moderate to good enantioselectivities (up to 55% and 93%, respectively). The pristine catalytic activity of the microreactor was intact even after 1 month.