Copper(I)-Catalyzed Boryl Substitution of 1-Trifluoromethyl Allenes for the Synthesis of 3-Boryl-Substituted 1,1--Difluorodienes.

A method to synthesize 3-boryl-1,1--difluorodienes via the copper(I)-catalyzed boryl substitution of trifluoromethyl-substituted allenes was developed. The borylated compounds were obtained up to 91% yield with excellent selectivity. We proposed that the reaction proceeded via γ-selective borylcupration into the trifluoromethyl-substituted allene, followed by copper(I)-β-fluoro elimination. Subsequent transformations of the borylation product by Suzuki-Miyaura cross-coupling or Diels-Alder reaction provided various compounds bearing a difluoro moiety, which are difficult to synthesize by existing methods.