Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

Enantiomerically pure 1,5‐hexadiene‐3,4‐diol, derived from D‐mannitol in a few steps, may serve as a starting material for enantiopure dihydropyrans and dihydrofurans bearing an unsaturated side chain which is amenable for further synthetic transformations. The synthesis relies on a ring size‐selective ring‐closing metathesis reaction of a triene. Most likely, a catalyst‐directing effect of an allylic hydroxy group is responsible for the selectivity.