Cyclization reactions of 1,6-dienes and 1,6-enynes by dual cobalt photocatalysis

Abstract

The merger of photocatalysis with cobalt catalysis has recently emerged as a powerful tool for implementing synthetically useful transformations under mild, environmentally friendly conditions. In this study, two triphenylamine-derived organo-photocatalysts were prepared, and their photocatalytic capacity for promoting the [Co^III]–H-mediated cyclization reactions of 1,6-dienes and 1,6-enynes was investigated. Photophysical and electrochemical studies indicate that these two photocatalysts possess strong reducing capability in the excited state, which can be exploited to convert Co(dmgH)(dmgH₂)Cl₂ into the corresponding [Co^III]–H species with ascorbic acid or i-Pr₂NEt as the reductant under blue light irradiation. This dual catalytic system can enable the cycloisomerization of 1,6-dienes and the reductive cyclization of 1,6-enynes to deliver an array of five-membered heterocyclic and carbocyclic compounds in good yields.