Visible‐Light Induced C(sp²)−H Amidation with an Aryl–Alkyl σ‐Bond Relocation via Redox‐Neutral Radical–Polar Crossover

Abstract

We report an approach for the intramolecular C(sp 2 )ÀH amidation of N-acyloxyamides under photoredox conditions to produce d-benzolactams with an aryl-alkyl sbond relocation. Computational studies on the designed reductive single electron transfer strategy led us to identify N-[3,5-bis(trifluoromethyl)benzoyl] group as the most effective amidyl radical precursor. Upon the formation of an azaspirocyclic radical intermediate by the selective ipso-addition with outcompeting an ortho-attack, radical-polar crossover was then rationalized to lead to the rearomative ring-expansion with preferential C À C bond migration.Scheme 1. Radical-polar crossover to access rearomative cyclization products via a radical ipso-addition.

Metal-free hypervalent iodine-promoted tandem carbonyl migration and unactivated C(Ph)–C(Alkyl) bond cleavage for quinolone scaffold synthesis

“…Then, 5-ipso trig cyclization of N -centered radical IIIb is significantly favored compared to that of the 6-endo trig cyclization to form a spirocyclic radical intermediate IV due to the steric hindrance. 23 i This observation is in line with the only carbonyl migration products obtained in the system. Finally, in path a, the abstraction of R 1 from species IV in the concurrence of the carbonyl migration regenerated the aromatic system to furnish the major product 2 , followed by the R 1 radical reacting with dichloroethane to deliver the side product R 1 Cl.…”

“…Based on the results above and related literature, 13 c ,23 we proposed a plausible mechanism in Scheme 5. Initially, a ligand exchange between the substrate 1 and PIDA furnished the intermediate I .…”

Organophotocatalytic N–O Bond Cleavage of Weinreb Amides: Mechanism-Guided Evolution of a PET to ConPET Platform

“…Further advances in this field derive from photoredox catalysis-based methods, which mitigate the need for toxic reagents, thereby enabling the mild generation of open shell reactive species . A valuable contribution has been the introduction of very effective O -substituents (N–OAr, OAr = 2,4-dinitrophenol, N–OC­(O)­Ar, Ar = 3,5-bis trifluoromethyl phenyl) (Figure D): this enables N–O bond cleavage to be achieved upon irradiation with eosin Y in the presence of 1,4-cyclohexadiene, for hydrogen-atom transfer (HAT), using green LEDs or using an iridium photoredox catalyst . The resulting amidyl radicals may then be intercepted through sequential cyclization or arylation events.…”

Electrochemically-promoted synthesis of benzo[b]thiophene-1,1-dioxides via strained quaternary spirocyclization

“…10 The group of Chang showcased an approach of visible-light-induced selective C(sp 2 )-H amidative cyclization to furnish d-benzolactams via selective ipso-addition of amidyl radicals (Scheme 1c). 11 On the other hand, organic electrochemistry has attracted broad interest as an enabling synthetic tool by the advantages of Scheme 1 The developed strategy involving an ipso-attack pathway (a-e).…”

“… 10 The group of Chang showcased an approach of visible-light-induced selective C(sp 2 )–H amidative cyclization to furnish δ-benzolactams via selective ipso -addition of amidyl radicals ( Scheme 1c ). 11 …”