Carbon−Carbon Coupling Reactions Catalyzed by Heterogeneous ...

Heterogeneous Pd Catalyzed C−C Coupling Reactions Chemical Reviews, 2007, Vol. 107, No. 1 163
Table 69. Pd/C-Catalyzed Ullmann-Type Coupling of Aryl
Halides in the Presence of CO2 210
entry Ar-X t a (h) yield b (%)
1 c Ph-I 15 27
2 d Ph-I 15 41
3 Ph-I 8 > 99
4 e Ph-I 8 65
5 4-Me-Ph-I 15 95
6 2-Me-Ph-I 24 87
7 4-MeO-Ph-I 15 97
8 4-CF3-Ph-I 48 95
9 1-Naph-I 24 100
10 Ph-Br 15 91
11 4-MeO-Ph-Br 24 95
12 4-Me2N-Ph-Br 48 85
13 2,6-di-MeO-Ph-Br 72 78
14 f 2-OH-1-Naph-Br 48 81
15 Ph-Cl 36 56
16 g Ph-Cl 36 96
17 g 3,5-di-MeO-Ph-Cl 48 81
18 g 1-Naph-Cl 36 95
19 g 3-EtO2C-Ph-Cl 96 93
a Reaction conditions: ArX (2 mmol); 5% w/w Pd/C (300 mg); Zn
(170 mg); H2O (5 mL); CO2 (1.0 MPa). b Isolated yields. c In the
absence of CO2. d CO2, 1 atm, bubbling. e CO2, 6.0 MPa. f 2-Naphthol
was obtained in 17% yield. g 5% Pd/C (400 mg).
Table 70. Ullmann-Type Coupling Reactions of Aryl Halides
with Pd/C and In
biaryl
product 174 t (h) yielda (%)
(1-Naph)2 2.5 87
(4-n-Bu-Ph)2 2.5 85
(4-MeO-Ph)2 2.5 91
(3-MeO-Ph)2 2.5 86
(4-HO-Ph)2 2.5 87
(4-EtO2C-Ph)2 2 88
(3-EtO2C-Ph)2 2.5 86
(4-F3C-Ph)2 2 92
(2-F3C-Ph)2 2.5 85
(4-CHO-Ph)2 3 87
(4-Ac-Ph)2 2.5 88
(4-Cl-Ph)2 2 91
(2-thienyl)2 1.5 92
(2-Py)2 1.5 86
(3-Py)2 3 89
a Isolated yield.
Scheme 50. Pd/C-Catalyzed Homocoupling of Aryl Iodide
175 in the Presence of Et3N
dehydrogenative homocoupling of pyridines. This is the
simplest and most efficient method. In the early 1960s, Pd/C
was extensively applied as a catalyst to synthesize bipyridine
by oxidative coupling of pyridine in the absence of base or
additives. 218-220 In 1971, a series of 2,2′-bipyridines 187 and
2,2′:6′,2′′-terpyridines 188 were prepared by refluxing alkylpyridines
186 in the presence of 5% Pd/C catalyst (Table
74). 221
Table 71. Synthesis of Butadienes by Pd/C-Catalyzed Coupling
of Vinyl Halides
entry R 1 R 2 yield a (%)
1 n-Hex H 92
2 Ph H 93
3 Ph H 89
4 4-MeO-Ph H 87
5 3-NH2-Ph H 79
6 3-HO-Ph H 72
7 2-Cl-Ph H 89
8 4-F3C-Ph H 88
9 4-Br-Ph H 88
10 4-Py H 89
11 H Ph 91
a Isolated yield.
Table 72. Intramolecular Vinyl and Aryl Coupling Reactions a
a Reaction performed in the presence of 2.5 mol % of Pd/C, 50 mol
% In and 1.5 equiv of LiCl in DMF (0.5 M) at 100 °C. b Isolated yield.
c 0.05 M LiCl in DMF was used.
Table 73. Pd/C-Catalyzed Suzuki-Type Homocoupling of
Arylboronic Acids
a Isolated yield.
In recent years, the Pd/C-catalyzed dehydrogenative
coupling of pyridines was widely applied to the synthesis