Di- and tetrahydropyrans with orthogonally protected hydroxymethyl side chains: a synthetic route and the structure elucidation of an unexpected acetal cleavage product

A synthesis of dihydropyrans with orthogonally protected hydroxymethyl side chains is presented in this contribution. Key steps of the synthesis are the regioselective epoxide opening using vinyl cuprate reagents, selective protection of primary alcohols and ring closing metathesis. A strategy based on the intermediate formation of a rigid bicyclic acetal turned out to be unsuccessful due to the unexpected formation of an annellated furanopyran rearrangement product . Elucidation of the structure was achieved using one- and two-dimensional NMR-methods.