Photocarboxylation of remote C–H bonds through nitrogen-centred radical 1,5-hydrogen atom transfer

Abstract

The carboxylation of the C−H bond utilizing CO2 represents a challenging but attractive tactic for capitalizing on the abundant availability of CO2 in organic synthesis. In this investigation, we report...

Visible-Light-Induced Transition-Metal-Free Redox-Neutral Carboxylation of Remote Benzylic C(sp3)–H Bonds via 1,5-Hydrogen Atom Transfer

“…Based on the control experiments and previous studies, a plausible mechanism for the overall transformation is proposed and outlined in Figure . First, the photocatalyst 4CzIPN, upon photoexcitation, would oxidize α-oxiamido acid 1a , delivering amidyl radical I through fragmentation.…”

“…However, to the best of our knowledge, there are few reports on the recovery of carbon dioxide intramolecularly. Inspired by our previous work 41 and the Leonori group's work, 7 we have designed and synthesized a series of benzylic αoxiamido acids for the first time. With these substrates, we developed visible-light-induced transition-metal-free redoxneutral carboxylation of remote benzylic C(sp 3 )−H bonds (Figure 1c).…”

Visible-Light-Driven Coupling of 1,3,4-Oxadiazoles and Hydroxamic Acid Derivatives

“…After investigating the literature, we found that hydroxamic acid derivatives have been widely used as nitrogen-centered radical precursors to prepare remote inert C­(sp 3 )-H functionalized products through visible-light-induced 1,5-hydrogen atom transfer (1.5-HAT). − As part of our ongoing interest in synthesizing useful skeletons via photoredox catalysis, we reported herein a C­(sp 3 )–C­(sp 3 ) radical–radical cross-coupling reaction for the preparation of α-alkylated 5-aryl-1,3,4-oxadiazole-2-methylamine derivatives with amide groups, which was characterized by broad substrate scope, good functional group compatibility, and no requirement of any base or metal (Scheme C).…”

Base- and metal-free visible-light driven site-selective α-C(sp3)–H functionalization reaction of glycine derivatives with hydroxamic acid derivatives

“…Due to the weak N–O bond, hydroxamic acid derivatives have recently been employed as N-radical precursors, which can be converted to the corresponding C-radicals via 1,5-hydrogen atom transfer processes and thus functionalize remote inert C(sp 3 )–H bonds with good regioselectivity and chemoselectivity (Scheme 1b). 27–30 In light of our continuous interest in visible-light-mediated radical–radical cross-coupling reactions, we wondered whether hydroxamic acid derivatives could couple with N -phenyl glycine derivatives for the synthesis of α-C(sp 3 )–H functionalized unnatural amino acids and peptides with amide groups. After exploration, we report herein the visible-light-induced radical–radical cross-coupling reactions of hydroxamic acid derivatives with N -phenyl glycine derivatives (Scheme 1c).…”