gem-Difluoro-Masked o-Quinone Methides Generated by Photocatalytic Radical (3+3) Annulation and Their (4+1) Cycloaddition with Sulfur Ylides.

A visible light-promoted radical (3+3) annulation of vinyldiazo compounds and bromodifluoromethyl alkynyl ketones for the construction of gem-difluoro-masked o-quinone methides (o-QMs) is described. The reactivity of this new type of o-QM precursor is demonstrated by its (4+1) cycloaddition with sulfur ylides, affording monofluorinated aromatic benzofurans by the elimination of HBr without external oxidants.