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.

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

“…20 yl phenyl) (Figure 1D): this enables N−O bond cleavage to be achieved upon irradiation with eosin Y in the presence of 1,4cyclohexadiene, for hydrogen-atom transfer (HAT), using green LEDs 21 or using an iridium photoredox catalyst. 22 The resulting amidyl radicals 23 may then be intercepted through sequential cyclization or arylation events. Importantly, the redox handle (e.g., 2,4-dinitrophenol) is critical to the success of these processes, where it serves to lower the reduction potential of the substrate.…”

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

“…[20] 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 1D): This enables N-O bond cleavage to be achieved upon irradiation with eosin Y in the presence of 1,4-cyclohexadiene, for HAT, using green LEDs [21] or using an iridium photoredox catalyst. [22] The resulting amidyl radicals [23] may then be intercepted through sequential cyclization or arylation events.…”

Photoredox/Iron Dual-Catalyzed Insertion of Acyl Nitrenes into C–H Bonds

“…It is worth noting that an oxidative pathway releases amidyl radical through N−H bond cleavage, 6 while amidyl radical is formed in reductive protocols through N−O bond cleavage. 7 As we know, acyl nitrenes are versatile synthons in amidation reactions. 8 A series of well-documented nitrene precursors have been developed, mainly including azides, sulfonamides, iminoiodinanes, dioxazoles, etc.…”

“…To confirm our assumption that the reaction involved an acyl nitrene intermediate, the reactions with S-or P-containing substrates were exploited under standard conditions. As expected, triphenylphosphine (6), diphenylsulfane (7), and (methylsulfinyl)benzene (8) were good reaction partners. The corresponding products 9, 10, and 11 were obtained in 75%, 54%, and 50% yield, respectively.…”