An elegant approach for stereocontrolled synthesis of furopyran building blocks

An elegant approach for stereocontrolled synthesis of furopyran (hexahydro-2H-furo3,2-b]pyran) building blocks was reported. The key steps in the sequence involved an efficient intramolecular 3-oxidopyrylium-alkene 5+2] cycloaddition for the synthesis of cycloadduct 6 and Beckmann fragmentation of ketoxime 13 to yield the furopyrans (5a-c).