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

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 [CoIII]-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 [CoIII]-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. Two triphenylamine-derived organophotocatalysts were developed. Their photocatalytic capacity was exploited to enable the [CoIII]-H-mediated cycloisomerization of 1,6-dienes and reductive cyclization of 1,6-enynes under visible light irradiation.