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

Abstract

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 as the only byproduct. Remarkably, high regioselectivity and trans diastereoselectivity can be achieved in this transformation even if the Z/E mixture of alkenes were employed.

Design and application of aminoacridinium organophotoredox catalysts

“…Extending the application of their dual catalytic cobalt/ acridinium salt process, the same group also performed a photooxidative [4+2] annulation between aromatic ketimine derivatives and styrenes (Scheme 12). 39,40 The SET oxidation of the alkene substrate by the excited Mes-Acr-Me + catalyst thereby produces a radical cation that reacts with the nucleophilic aromatic ketimine to give a stable benzylic radical intermediate. A subsequent sequence consisting of a cyclization, oxidation and deprotonation allows to obtain highly substituted 3,4-dihydroisoquinolines with excellent trans diastereoselectivity.…”

Photoelectrochemical Cells for Artificial Photosynthesis: Alternatives to Water Oxidation

“…Subsequently, by combining photoredox and cobaloxime catalysis, the same group reported the oxidative [4+2] annulation reaction of imines with styrenes to form multi‐substituted 3,4‐ dihydroisoquinoline derivatives (Figure d) . A radical cation intermediate was generated from the oxidation of styrene by the photosensitizer, which underwent nucleophilic attack by an imine to form a benzyl radical intermediate, followed by eventual ring closure to give the dihydroisoquinoline product.…”

Facilitating a high‐performance photocatalyst for Suzuki reaction: Palladium nanoparticles immobilized on reduced graphene oxide‐doped graphitic carbon nitride

“…With the development of photocatalysis technology, light‐driven chemical reactions are becoming increasingly noticeable and have been shown as a crucial way for pursuing environmentally benign, green synthetic and sustainable processes . Many studies centered on the development of efficient catalysts for visible‐light‐driven Suzuki coupling reactions, including the GO‐Pd@Ag‐AgBr and Pd@NH 2 ‐UiO‐66 catalysts .…”