Chemistry Reference
In-Depth Information
[RhCl(coe)
2
]
2
,
Cy
3
P.HCl,
Δ
+
N
N
3.41
3.42
Scheme 3.23
Cl
(OC)
2
Rh
Rh(CO)
2
Cl
N
CO
CO
3.38
X
Rh
N
3.43
X = Cl or Br
OC
CO
CO
CO
OC
N
Rh
N
Rh
X
Br
Rh
CO
X
H
Ar
N
3.44
3.45
3.40
HX
OC
CO
OC
CO
Rh
Rh
N
N
Br
Ar
3.47
3.46
ArBr
Scheme 3.24
A similar mechanism may operate in related reactions, such as a vinylation of azoles
3.48
using an eco-
nomical cobalt catalyst (Scheme 3.25), generated
in situ
,
21,22
as well as a ruthenium-catalysed carbonylative
coupling of imidazoles
3.50
(Scheme 3.26).
23
An extension of this concept is the coupling of two molecules by double C-H activation; two hydrocarbons
coupling with formal elimination of H
2
.
24
This is possible under the right circumstances. Thiophenyl and
other heteroaryl derivatives of caffeine
3.54
could be produced in this way (Scheme 3.27).
25
The reaction
shows surprising selectivity for the coupling of the two different heterocycles over dimerization of either
CoBr
2
, DPEphos,
Me
3
SiCH
2
MgCl
Pr
Pr
N
N
+
O
O
Pr
Pr
3.48
3.49
Scheme 3.25
