Computational S_N2-Type Mechanism for the Difluoromethylation of Lithium Enolate with Fluoroform through Bimetallic C−F Bond Dual Activation

The reaction mechanism for difluoromethylation of lithium enolates with fluoroform was analyzed computationally (DFT calculations with the artificial force induced reaction (AFIR) method and solvation model based on density (SMD) solvation model (THF)), showing an S_N2-type carbon–carbon bond formation; the “bimetallic” lithium enolate and lithium trifluoromethyl carbenoid exert the C−F bond “dual” activation, in contrast to the monometallic butterfly-shaped carbenoid in the Simmons–Smith reaction. Lithium enolates, generated by the reaction of 2 equiv. of lithium hexamethyldisilazide (rather than 1 or 3 equiv.) with the cheap difluoromethylating species fluoroform, are the most useful alkali metal intermediates for the synthesis of pharmaceutically important α-difluoromethylated carbonyl products.