An I2-catalyzed, Visible-Light Photoredox-Mediated Radical Conversion of a-Nitrocarbonyls to Nitrile Oxides. Catalytic Access to Isoxazolines and Isooxazoles from Alkenes and Alkynes

A visible light-mediated, I2-catalyzed intermolecular transformation of alkenes, conjugated dienes, styrenes and alkynes to isooxazoline and isoxazole motifs with a-nitrocarbonyls and analogs is reported. The reaction is also applicable to 1,1-disubstituted terminal, 1,2-disubstituted internal and trisubstituted alkenes, and tolerates a range of functional groups including epoxides, heterocycles, phosphates, free alcohols and thiocyanates. Mechanistic studies reveal that a-nitrocarbonyls are first converted to -carbonyl radicals followed by their conversion to acyl nitrile oxides, which subsequently undergo [3 + 2] dipolar cycloaddition reactions with the unsaturated molecules.