Relay Organophotoredox/N-Heterocyclic Carbene Catalysis-Enabled Asymmetric Synthesis of Dibenzoxazepine-Fused Pyrrolidinones

Abstract

An unprecedented highly stereoselective synthesis of pyrrolo­[1,2-d]­[1,4]­oxazepin-3­(2H)-ones has been accomplished via photoredox/N-heterocyclic carbene (NHC) relay catalysis. A wide range of substituted dibenzoxazepines and aryl/hetereoaryl enals were well accommodated under the organic photoredox catalysis-promoted amine oxidation to generate the imines, followed by a NHC-catalyzed [3 + 2] annulation reaction to achieve excellent diastereo- and enantioselectivities of the dibenzoxazepine-fused pyrrolidinones.

Recent Progress in Transformations of Azepine/Oxazepine/Thiazepine Derivatives

“…In 2023, in another visible light approach, the Chauhan laboratory investigated a synergy effect between eosin Y photocatalyst and NHC organocatalyst in (3+2)‐annulation of dihydrodibenzo[ b , f ][1,4]oxazepines 15 and enals 59 (Scheme 23). [46] Considering the toxicity dibenzoxazepine 1 , Chauhan succeeded in designing a new asymmetric method for the elimination of direct use of dibenzoxazepine 1 . Of course, this compound was produced during the reaction process.…”

Recent advances in combining photo- and N-heterocyclic carbene catalysis

“…20 Recently, the Chauhan group developed a stereoselective strategy to access pyrrolo[1,2-d][1,4]-oxazepin-3(2H)-ones (Scheme 16). 21 Imine is formed upon one-electron oxidation, hydrogen atom transfer, and proton transfer of amine. Then the imine intermediate enters into the NHC catalytic cycle, where the Breslow intermediate acts as the homoenolate equivalent, which aer tautomerization undergoes nucleophilic addition to imine to forge acyl azolium species.…”