First evidence for the formation of a geminal dizinc carbenoid: a highly stereoselective synthesis of 1,2,3-substituted cyclopropanes.

Significant amounts of novel gem-dizinc carbenoids (RZnCHIZnR) are formed when diethylzinc is mixed with iodoform in CH2Cl2 at 0 degrees C. This reagent was shown to be effective in the cyclopropanation of butenediol derivatives to generate a cyclopropylzinc intermediate that could be trapped with a variety of electrophiles. 1,2,3-Substituted cyclopropane derivatives are formed with excellent diastereoselectivities by using this simple procedure.