A one-pot tandem SN2-Michael addition sequence has been developed for the preparation of five-memberedand six-membered-ring nitrogen and sulfur heterocycles from 6-or 7-halo-2- alkenoate esters. Nitrogen-containing rings are prepared by reaction of the w-halo-2- alkenoate eater 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 ...