Visible-light-mediated copper photocatalysis for organic syntheses

Abstract

Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C-H functionalization that have been reported over the past 5 years, are included.

Keywords: copper-photocatalyzed reactions; green chemistry; mechanisms of copper photocatalysis; photoinduced copper-based catalysis; photoredox catalysis; special features of copper photocatalysis.

Scheme 1

Photoredox catalysis mechanism of [Ru(bpy)₃]²⁺.

Scheme 2

Photoredox catalysis mechanism of Cu^I.

Scheme 3

Ligands and Cu^I complexes.

Scheme 4

Mechanism of Cu^I-based photocatalysis.

Scheme 5

Mechanisms of Cu^I–substrate complexes.

Scheme 6

Mechanism of Cu^II-base photocatalysis.

Scheme 7

Olefinic C–H functionalization and allylic alkylation.

Scheme 8

Cross-coupling of unactivated alkenes and CF₃SO₂Cl.

Scheme 9

Chlorosulfonylation/cyanofluoroalkylation of alkenes.

Scheme 10

Hydroamination of alkenes.

Scheme 11

Cross-coupling reaction of alkenes, alkyl halides with nucleophiles.

Scheme 12

Cross-coupling of alkenes with oxime esters.

Scheme 13

Oxo-azidation of vinyl arenes.

Scheme 14

Azidation/difunctionalization of vinyl arenes.

Scheme 15

Photoinitiated copper-catalyzed Sonogashira reaction.

Scheme 16

Alkyne functionalization reactions.

Scheme 17

Alkynylation of dihydroquinoxalin-2-ones with terminal alkynes.

Scheme 18

Decarboxylative alkynylation of redox-active esters.

Scheme 19

Aerobic oxidative C(sp)–S coupling reaction.

Scheme 20

Copper-catalyzed alkylation of carbazoles with alkyl halides.

Scheme 21

C–N coupling of organic halides with amides and aliphatic amines.

Scheme 22

Copper-catalyzed C–X (N, S, O) bond formation reactions.

Scheme 23

Arylation of C(sp²)–H bonds of azoles.

Scheme 24

C–C cross-coupling of aryl halides and heteroarenes.

Scheme 25

Benzylic or α-amino C–H functionalization.

Scheme 26

α-Amino C–H functionalization of aromatic amines.

Scheme 27

C–H functionalization of aromatic amines.

Scheme 28

α-Amino-C–H and alkyl C–H functionalization reactions.

Scheme 29

Other copper-photocatalyzed reactions.

Scheme 30

Cross-coupling of oxime esters with phenols or amines.

Scheme 31

Alkylation of heteroarene N-oxides.