BR+-INDUCED CYCLIZATION OF GAMMA,DELTA-UNSATURATED KETONES - A NEW APPROACH TO BROMOPYRAN DERIVATIVES

3,5-dibromo-3,4-dihydro-2,2-dimethyl-(2H)-pyrans 2, are obtained through a simple and new procedure involving a bromoenol-etherification of gamma,delta-unsaturated ketones 1; the key step is the formation of mono-bromopyran intermediate A.