Multicomponent Synthesis of α-Branched Tertiary and Secondary Amines by Photocatalytic Hydrogen Atom Transfer Strategy

Abstract

A multicomponent carbonyl alkylative amination reaction is described. A variety of N-arylamines, aldehydes, and hydrocarbons have been examined as reaction substrates using tetrabutylammonium decatungstate as photocatalyst, providing the corresponding α-branched tertiary and secondary amines in good to moderate yields. The reaction proceeds through the generation of alkyl radicals by a light-promoted hydrogen atom transfer process followed by free radical addition to iminium ions generated in situ.

Multicomponent reactions and photo/electrochemistry join forces: atom economy meets energy efficiency

“…226 In a recent complementary strategy, Qi et al focused on the use of unactivated alkanes as the radical source for the alkylation of in situ formed imines. 227 Violet irradiation of tetrabutylammonium decatungstate (TBADT; [W 10 O 32 ] (nBu 4 N) 4 ) is known to enable radical generation through the HAT of strong aliphatic bonds. This photocatalyst was therefore used to form mainly tertiary but also secondary amines.…”

C-centered radical-initiated cyclization by directed C(sp3)–H oxidative functionalization

“…In the same year, the potassium persulfate-promoted cyclization of 1,3-diketone and styrenes was reported by Guo's group, 32 where potassium persulfate was utilized to oxidize the C(sp 3 )–H of 1,3-diketone, and the corresponding C-radical was cyclized with styrenes. Because visible-light photoredox catalysis has become a mild and valuable platform for the development of a wide range of radical reactions, 33 Zhou's group 34 demonstrated a new visible light-mediated cyclization of tertiary amines with α-trifluoromethyl styrenes to construct fluorinated tetrahydropyridines and azabicyclo[3. m .1] frameworks and achieved two consecutive C–F substitutions in one-pot (Scheme 12).…”

Decatungstate-photocatalyzed direct coupling of inert alkanes and quinoxalin-2(1H)-ones with H2 evolution

“…Recently, TBADT-involved photocatalytic strategies have been applied in acylation reactions, 14 hydroacylation reactions, 15 hydroalkylation reactions, 16 C(sp 3 )–H fluorination reactions, 17 etc . 18 For alkylation reactions, the TBADT-photocatalyzed alkylation of halides, 19 alkenes, 20 methanesulfonylalkynes 21 were also reported. However, TBADT-photocatalyzed alkylation of heterocycles has rarely been reported.…”