Visible-light induced dearomative cascade cyclization of aryl-ynones/N-arylpropiolamides to phosphorothiolated spiro[5.5] and azaspiro[4.5]trienones

Abstract

Herein, we report a visible-light-induced radical ring annulation approach through an arene radical cation intermediate of biaryl ynones, providing an important template towards synthesis of varied 3D spirocyclic frameworks. This transformation includes consecutive nucleophilic sulphur addition to the alkyne bond, followed by 6-exo-trig addition of a vinyl radical for the synthesis of diverse thiophosphorylated spiro[5.5] and azaspiro[4.5]trienones with high functional group tolerance. This transition-metal and stoichiometric oxidant-free methodology was also applicable under sunlight irradiation. The reaction efficiency was significantly improved under continuous-flow conditions, and this establishes a general platform for spirocycle synthesis by functionalization of C–C alkyne bonds, expanding the reach of radical cation intermediates with nucleophiles.