Regioselectivity of Mercury-Promoted Oxacyclizations of Alkynyl Diols

Abstract

Hg(OTf)2-catalyzed cyclization of an alkynyl alcohol on a tetra­hydropyran template gives the bispyranyl ketone arising from dehydrative cyclization and alkyne hydration, rather than the targeted fused pyran-oxepane product. The combination of stoichiometric Hg(OTf)2 and triethylsilane gives reductive cyclization, but affords the fused pyran-oxocane corresponding to an 8-endo-mode oxacyclization process.