A new method for the synthesis of bicyclic pyran acetals

Abstract magnified image cis ‐Fused bicyclic acetals were obtained from the unusual cyclization reaction between diols and dihydropyran. Furothiopyran, substituted pyranopyrans, and pyranooxepine and pyranobenzoxepine compounds were obtained with high diastereoselectivity and cis ‐diastereomers were obtained in high yields.