Direct sp³ CH Amination of Nitrogen‐Containing Benzoheterocycles Mediated by Visible‐Light‐Photoredox Catalysts

Abstract

Visible-light-mediated direct sp(3) C-H amination of benzocyclic amines via α-aminoalkyl radicals by using photoredox catalysts is described here. The obtained N,N-acetals were also successfully applied for carbon-carbon bond forming reactions with carbon nucleophiles. The procedure is suitable for a late-stage modification of C-H bonds to C-C bonds.

Photoredox Catalysis in Organic Chemistry

“…31 Here, radical–radical coupling reactions occur between α-amino radicals and the radical anion derived from single-electron reduction of di- tert -butyl azodicarboxylate. Following on from early work by Reiser and Pandey (Scheme 6b), the Rueping, Yoon, and Nishibayashi groups independently reported protocols for redox-neutral α-alkylations of N -arylamines.…”

The chemistry of amine radical cations produced by visible light photoredox catalysis

“…The Nishibayashi group also successfully trapped α-amino radicals derived from N -aryltetrahydroquinolines and N -arylindolines using di- tert -butyl azodicarboxylate 110 to form N , N -acetal products 111 (Scheme 26) [93]. Functionalization of the sp 3 C–H bond α to the nitrogen atom in tetrahydroquinolines and indolines via iminium ions is challenging because the corresponding iminium ions are enolizable and thus tend to tautomerize to enamines [94–95] and/or aromatize [96–97].…”

Photoredox α-Vinylation of α-Amino Acids and N-Aryl Amines

“…5,6 Generation of α-amino radicals under photoredox conditions typically proceeds via single-electron oxidation of an amine and subsequent deprotonation of the resulting radical cation. 4,5 Recently, our group has also reported an alternative strategy for α-amino radical formation via the decarboxylation of N - tert -butoxycarbonyl ( N -Boc) α-amino acids, 7,8 a CO 2 -extrusion mechanism that has implications for the use of biomass feedstocks in conjugate additions and organometallic couplings.…”