173
5.2.2 Carbon-Heteroatom Cross-Coupling Reactions
5.2.2.1 C-S Cross-Coupling
CCHE reactions are also a powerful tool to construct C-X bonds. In this respect, the
study of C-S bond formation reactions is a fundamental research area, because the
introduction of sulfur atoms is a crucial step in the synthesis of many pharmaceuticals and bioactive molecules. In 2014, Lei and Wu’s groups developed an efficient
intramolecular CCHE reaction to synthesize benzothiazoles 64 from
N-phenylbenzothioamides 61 without any oxidant (Scheme 5.27). This transformation was promoted by photosensitizer Ru(bpy) 3 (PF 6 ) 2 and HEC Co(dmgH) 2 pyCl
N
H
Ph
COOEt
H
N
H
COOEt
Ph +
H 2
Ir(ppy) 3 , Co(dmgH) 2 (COOMePy)Cl
N 2 , 450 nm LED, 5 h
55
60
R
R
N
H
COOEt
N
H
COOEt
N
H
COOEt
F
O
N
H
COOEt
N
H
COOEt
N
H
CONHPh
OMe
60a, 93 %
60b, 90 %
60c, 80 %
60d, 93 %
60e, 95 %
60f, 55 %
Scheme 5.24 Synthesis of indoles via a photocatalytic CCHE strategy
Scheme 5.25 The reaction of 55a with a radical scavenger
5 Fourth-Generation Oxidative Cross-Coupling Reactions