Ring-size-selective enyne metathesis as a tool for desymmetrization of an enantiopure C2-symmetric building block.

The enantiomerically pure C(2)-symmetrical hexa-1,5-diene-3,4-diol is selectively monopropargylated. The products undergo ring-closing enyne metathesis to give exclusively dihydropyrans as single stereoisomers. An unprotected hydroxy group is identified as the factor controlling the ring-size selectivity.