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

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