Ring-Size-Selective Enyne Metathesis as a Tool for Desymmetrization of an Enantiopure C2-Symmetric Building Block

The enantiomerically pure C-2-syrnmetrical 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.