A TANDEM ESTER CLEAVAGE-MICHAEL ADDITION-REACTION FOR THE SYNTHESIS OF OXYGEN HETEROCYCLES

A tandem ester cleavage-Michael addition sequence has been developed for the preparation of five- and six-ring oxygen heterocycles bearing an acetic acid residue at C-2. Treatment of ethyl 6- or 7-acetyloxy-2-alkenoates with ethanolic sodium ethoxide affords the tetrahydrofuran and tetrahydropyran products in 70-90% yields. The reaction is clean and appears to be a general route for the preparation of these compounds. Steric hindrance to the initial acetate cleavage and unfavorable entropy in closing large rings appear to be the only limitations to the procedure.