An Improved gem-Dimethylcyclopropanation Procedure Using Triisopropylsulfoxonium Tetrafluoroborate

A new procedure for the cyclopropanation of α,β-unsaturated carbonyl compounds and related systems is described which employs triisopropylsulfoxonium tetrafluoroborate and sodium hydride in dimethylformamide. Using this reagent, a range of α,β-unsaturated ketones (and an ester and a vinyl nitro example) has been converted into the corresponding gem-dimethylcyclopropyl carbonyl compounds; in addition, a preliminary result is described in which an activated alcohol is converted directly into a gem-dimethylcyclopropyl ketone by a one-pot tandem oxidation-cyclopropanation sequence, albeit in low yield.