Co2(CO)8-mediated Endo Mode Cyclization of Epoxy-alcohol: Synthesis of 2-Ethynyl-3-hydroxy-2-methyltetrahydropyran and 2-Ethynyl-3-hydroxy-3-methyltetrahydropyran Derivatives.

Successive treatment of 4,5-epoxy-5-methyl-7-trimethylsilyl-6-heptyne-1-ol with Co2(CO)8 at 0 degrees C and a catalytic amount of BF3 x OEt2 at -78 degrees C gave the tetrahydropyran derivatives with the cobalt-complexed moiety. Similarly 4,5-epoxy-4-methyl-7-trimethylsilyl-6-heptyne-1-ol underwent ring closure under the above conditions to provide the corresponding tetrahydropyran derivatives. The preferential endo mode cyclization over the exo one was observed in these experiments.