Co-2(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 Co-2(CO)(8) at 0 degreesC and a catalytic amount of BF3. OEt2 at -78 d egreesC gave the tetrahydropyran derivatives with the cobalt-complexed moie ty. Similarly 4,5-epoxy-4-methyl-7-trimethylsilyl-6-h-heptyne-1-ol underwen t ring closure under the above conditions to provide the corresponding tetr ahydropyran derivatives. The preferential endo mode cyclization over the ex o one was observed in these experiments.