Preparation of chiral DMAP derivatives and investigation on their enantioselective catalytic activity in benzazetidine synthesis and kinetic resolutions of alcohols

Abstract

4-dimethylaminopyridine (DMAP) is an extremely versatile catalyst active in a large series of chemical transformations because of its relevant basicity and nucleophilicity. In this paper, we present the synthesis of two chiral DMAP derivatives starting from 4-halopyridine and l-proline benzyl ester. The key steps of these preparations are a ZnII-coordinated dimer of proline ester and a variation of the Buchwald-Hartwig promoted by copper(I) salts. The preparation of these compounds was achieved with the use of inexpensive materials and facile procedures and does not require the use of any catalyst based on transition metals. In addition, these procedures open up the way for the preparation of a large variety of chiral DMAP organocatalysts. Their catalytic activity was tested in t-butoxycarbonyl transfer reactions, chosen as a benchmark because these transformations potentially profit from the presence of a nucleophilic catalyst. The kinetic resolution of alcohols and the enantioselective preparation of benzazetidines, in some experiments, was achieved with a noticeable enantiomeric ratio.