A STEREOSPECIFIC ANIONIC REDUCTION OF GEM-BROMOHALOCYCLOPROPANES BY THE DIMSYL ANION

The reaction of several ,2,3,3-tetrasubstituted-gem-bromohalocycloprop anes with t-BuOK in DMSO unexpectedly yielded the monohalocyclopropane s in good yield. A closer investigation revealed that this reaction mu st be initiated by a nucleophilic attack by the dimsyl anion (CH3SOCH2 -) on bromine with subsequent protonation of the carbenoid intermediat e. The reaction occurs rapidly (within 2 minutes) and is not inhibited by radical scavengers or in the dark. Only bromine, and not chlorine, is reduced, and the intermediate cyclopropyl anion is configurational ly stable under the reaction conditions.