Visible‐Light‐Promoted Iminyl‐Radical Formation from Acyl Oximes: A Unified Approach to Pyridines, Quinolines, and Phenanthridines

Abstract

Aunified strategy involving visible-lightinduced iminyl-radical formation has been established for the construction of pyridines,quinolines, and phenanthridines from acyl oximes.W ithf ac-[Ir(ppy) 3 ]asaphotoredox catalyst, the acyl oximes were converted by 1e À reduction into iminyl radical intermediates,w hich then underwent intramolecular homolytic aromatic substitution (HAS) to give the N-containing arenes.These reactions proceeded with ab road range of substrates at room temperature in high yield. This strategy of visible-lightinduced iminyl-radical formation was successfully applied to afive-step concise synthesis of benzo[c]phenanthridine alkaloids.Scheme1. N À Oc leavage of acyl oximes to form N-containing heterocycles. MW = microwave radiation.

Transition Metal‐Catalyzed Reactions Involving Oximes

“…In 2015, Zhang and Yu et al. demonstrated the ability of a light‐promoted iminyl radical from acyl oximes to construct heteroarenes with nitrogen‐containing six‐membered rings via intermolecular cyclization (Scheme and Scheme ) . The fac ‐[Ir(ppy) 3 ] was adopted as a photocatalyst which could be promoted to the excited state with visible light.…”

Catalytic N-radical cascade reaction of hydrazones by oxidative deprotonation electron transfer and TEMPO mediation

“…As the notable early studies by MacMillan 17 and Sanford 18 on neutral N-centred radical-mediated photocatalytic C–H amination of aldehydes and (hetero)arenes, several promising visible-light photocatalytic protocols have been developed by other groups for generating N-centred radicals and C–N bond formation ( Fig. 1a ) 19 20 21 22 23 . Despite their advantages, these methods require the introduction of a photolabile substituent at the nitrogen atom as a handle for photo-activation.…”

Cu0‐Promoted Cyclisation of Unsaturated α‐Halogeno Amides To Give β‐ and γ‐Lactams

“…In the past decades, iminyl radicals have been demonstrated as valuable intermediates in organic transformations, because they can be trapped by aromatic ring or double bond to form a series of nitrogen containing heterocycles 9. Very recently, the first visible‐light promoted generation of iminyl radicals from acyl oximes was reported by Zhang and Yu, which were subsequently converted into pyridines, quinolines, and phenanthridines through a homolytic aromatic substitution (HAS) process 10. However, this intramolecular reaction requires several steps for the preparation of the substrates, which limited its applications in the organic synthesis.…”