Chemoselective additions of chloromethyllithium carbenoid to cyclic enones: A direct access to chloromethyl allylic alcohols

Chloromethyllithium carbenoid has been chemoselectively added to cyclic enones (5-, 6- and 7-membered systems, including two natural products) to provide chloromethyl allylic alcohols. Under the optimized reaction conditions neither concomitant (n+1) homologation nor conjugate addition or Simmons-Smith-like cyclopropanation takes place. The presence of LiBr is estimated to play a dual role, namely as a carbenoid stabilizer and mild Lewis acid activator of the C=O group. Notably, the mesomeric effect caused by β-heteroatom-containing substituents promotes the attack of the reagent at the most activated position.