Trimethylsilylpotassium. Deoxygenation of epoxides with inversion of stereochemistry

The reactions of silyl anions with appropriately substituted epoxides are potential stereospecific routes to diastereomerically pure erythro and threo-/3-alkoxysilanes. We report here that some mono-, di-, and trisubstituted epoxides can be deoxygenated in good yields stereospecifically with inversion of stereochemistry by trimethylsilylpotassium generated in situ. Reaction of cis and trans epoxides with hexamethyldisilane and potassium methoxide (KOMe) in anhydrous hexamethylphosphoric triamide (HMPT) at 65° under argon for 3 h affords the corresponding trans and cis olefins, respectively. Since olefins can be epoxidized with retention of stereochemistry, this constitutes a new olefin inversion procedure. The yields and stereospecificity of this deoxygenation reaction for several isomerically pure (>99%) epoxides5 are listed in Table I.