Regioselective and stereospecific formation of 2-ethynyl-3-hydroxytetrahydropyran derivatives via 6-endo ring closure

Abstract

Efficient access to tetrahydropyran derivatives via highly regio- and stereoselective 6-endo tet mode ring opening of an epoxide by an internal hydroxy group has been developed. Cobalt complexes, derived from trans-4,5-epoxy-6-heptyn-1-ols and dicobalt octacarbonyl were treated with a catalytic amount of BF 3·OEt 2 in CH 2Cl 2 at −78°C to afford cis-2-ethynyl-3-hydroxytetrahydropyran derivatives in a highly regio- and stereoselective manner. Similar treatment of cis-4,5-epoxides provided the corresponding trans-tetrahydropyrans selectively.