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.