Stereospecific annulation of hydroxy vinyl ethers in the presence of triflic anhydride and tertiary amines and its synthetic application are described. Each 1-hydroxy-2-oxabicyclo [n. 4.0] alkane, 2-oxabicyclo [n. 4.0] alk-1 (6)-ene and 2-oxabicyclo [n. 4.0] alk-1 (6+ n)-ene is stereoselectively synthesized from the same hydroxy vinyl ether depending on the choice of the reaction conditions (temperature, solvent and tertiaryamine). These compounds lead ...