Direct Arylation via C–H Activation - New Trends in Cross-Coupling: Theory and Applications - page 590

R 2 R 2

Ar Ar

Br [RuCl 2 (p-cymene) ] 2 (2.5 mol%)

PPh 3 (10 mol%)
KOAc (20 mol%)
K 2 CO 3 (4 equiv.)
H 2 O, 100 °C, 36 h

+

N R

N R

R 3

R 1 R 1

R=H,Me

Scheme 12.77 Ortho-diarylation of imine derivatives with the use of water in place
of NMP.

Br

[RuCl 2 (C 6 H 6 )] 2 (2.5 mol%)
PPh 3 (10 mol%)
K 2 CO 3 ,NMP,120°C,20h

N N N N

R

N N R

R

+

+

Ph

Ph Ph

1.2 equiv

combined yields mono : diphenylated

64%
90%
76%
84%
88%
0%

R= H

H(2.5equiv)
C(O)Me
C(O)t-Bu
C(O)Ph
Ts

31:69
0:100
89:11
86:14
77:23

Scheme 12.78 Ortho-arylation of imidazoline derivatives.

Br [RuCl 2 (C 6 H 6 )] 2 (2.5 mol%)

PPh 3 (10 mol%)
K 2 CO 3 ,NMP,120°C

O N O N

O N

+

+

Ph

Ph Ph

combined yields

mono : diphenylated

1.2 equiv Ph-Br
2.5 equiv Ph-Br

60%
100%

25:75
0:100

Scheme 12.79 Ortho-arylation of an oxazoline derivative.

2-arylimidazolines with an aryl bromide and [RuCl 2 (C 6 H 6 )] 2 as catalyst. 140
A mixture of mono- and bis-arylated products was obtained with a 31 : 69
ratio in the presence of 1.2 equiv. of phenyl bromide, whereas bis-arylated
product was obtained predominantly with 2 equiv. In order to synthesize the
mono-arylated product with appreciable yield, various N-substituted de-
rivatives were tested, where the introduction of bulky substituents on ni-
trogen proved critical. Notably, N-tosyl derivatives did not form any product
owing to the electron-withdrawing nature of the tosylate, which inhibits the
binding of the nitrogen with the metal center (Scheme 12.78).
The same method was also applied with 2-phenyloxazolines as sub-
strates. 140 A slight excess of the aryl bromide afforded a mixture of both
mono- and bis-arylated products. In this case, the bis-aryl product was ex-
clusively obtained with 2.5 equiv. of the aryl bromide (Scheme 12.79).