Photoredox streamlines electrocatalysis: photoelectrosynthesis of polycyclic pyrimidin-4-ones through carbocyclization of unactivated alkenes with malonates

Abstract

Both polycyclic pyrimidin-4-one synthesis and the dehydrogenative coupling of malonates often require a redox agent, an elevated temperature, large amounts of transition-metal salts, and/or highly acidic/basic conditions, and the promising photoelectrocatalysis suffers from limited reaction patterns. We present herein a new photoelectrocatalytic mode and an electrolysis–photocatalysis–Brønsted base hybrid system for the synthesis of polycyclic pyrimidin-4-ones through dehydrogenative carbocyclization of unactivated alkenes with simple malonates under very mild and external-oxidant-free conditions. The reaction exhibits a good functional-group tolerance and is amenable for a gram-scale synthesis, and the sunlight could serve as the light source. Mechanistic studies suggest that the synergistic effect of light and electricity originates from the fast anchoring of an active electrochemical intermediate by the oxidative quenching photocatalytic cycle of Ir(ppy)₃.