TANDEM SN2-MICHAEL REACTIONS FOR THE PREPARATION OF SIMPLE 5-MEMBERED AND 6-MEMBERED-RING NITROGEN AND SULFUR HETEROCYCLES

A one-pot tandem S(N)2-Michael addition sequence has been developed for the preparation of five-membered- and six-membered-ring nitrogen and sulfur heterocycles from 6- or 7-halo-2-alkenoate esters. Nitrogen-containing rings are prepared by reaction of the omega-halo-2-alkenoate ester with a primary amine in the presence of triethylamine. The sulfur analogues are generated by thiourea displacement of the halide followed by base hydrolysis of the isothiouronium salt. Yields are routinely in the 60-80% range. Experiments are described which elucidate the chronology of the reaction sequences. Ring size and steric hindrance to the initial substitution reaction appear to be the only limitations of the procedure.