Selective Oxidative [4+2] Imine/Alkene Annulation with H2 Liberation Induced by Photo-Oxidation

The oxidative [4+2] annulation reaction represents an elegant and versatile synthetic protocol for the construction of six-membered heterocyclic compounds. Herein, a photoinduced oxidative [4+2] annulation of NH imines and alkenes was developed by utilizing a dual photoredox/cobaloxime catalytic system. Various multisubstituted 3,4-dihydroisoquinolines can be obtained in good yields. This method is not only obviated the need of stiochiometric amounts of oxidants but also exhibited excellent atom economy by generating H-2 as the only byproduct. Remarkably, high regioselectivity and transdiastereoselectivity can be achieved in this transformation even if the Z/E mixture of alkenes were employed.