Thiol-Catalyzed Photodriven Stereoselective Hydrodifluoroacetylative Cyclization of Alkyne.

A metal-free protocol for visible-light-driven intramolecular hydrodifluoroacetylative cyclization of N-propargyl or N-homopropargyl-2-bromo-2,2-difluoroacetamide to α,α-difluorinated ß-substituted γ- or δ-lactam without an additional photosensitizer has been developed. By using thiol and Hantzsch ester as the catalyst and hydrogen donor, respectively, to implement a hydrogen atom transfer process, moderate to high (Z) selectivity was achieved. The results of a mechanistic investigation revealed the critical contribution of the thiol catalyst in attaining the stereoselectivity.