Photoinitiated ambient temperature copper-catalyzed atom transfer radical addition (ATRA) and cyclization (ATRC) reactions in the presence of free-radical diazo initiator (AIBN)

Abstract

The use of UV light in copper-catalyzed atom transfer radical addition (ATRA) and cyclization (ATRC) reactions of various (poly)halogenated compounds to highly active alkenes in the presence of AIBN is reported. Radicals generated from photodecomposition of AIBN efficiently regenerated the copper(I) complex at ambient temperature enabling ATRA of CCl₄ and CBr₄ with catalyst loadings as low as 0.05 mol-%. The desired monoadduct was obtained in lower yields in the ATRA of less active halogenated compounds, which was mostly due to incomplete alkene conversions. Ambient temperature ATRA of CCl₄ to various 1,6-dienes followed by sequential ATRC was also performed in the presence of UV light using [Cu^II(TPMA)Cl][Cl] complex and AIBN. High yields of the 5-exo-trig cyclic product were obtained for all dienes with preferential formation of the cis isomer.