Michael additions catalysed by cinchona alkaloids bound via their vinyl groups to preformed crosslinked polymers

Abstract

Cinchona alkaloids have been satisfactorily bound via their vinyl groups to crosslinked polymers containing thiol residues. The products have been used to catalyse one or more of the following Michael additions: the additions of (1) thio-p-cresol, (2)p-chlorothiophenol, and (3) thiobenzoic acid to cyclohex-2-en-1-one, and (4) of toluene-α-thiol to 2-nitrostyrene. The steric course of reactions (1)–(3) is dominated by the configurations of C-8 and C-9 in the alkaloids, but the nature of the C-3 group does have an effect and this probably explains why the optical yields obtained using the polymer-supported catalysts were lower than those obtained using the free alkaloids. The optical yields obtained in reaction (4), though small, did not follow this pattern. The polymers afforded higher optical yields than the free alkaloids and, in one case, the predominant enantiomer was of opposite configuration.