Chemistry Reference
In-Depth Information
O
O
Si(OEt)
3
RuH
2
(CO)(PPh
3
)
3
,
Δ
S
Si(OEt)
3
S
3.183
3.184
Scheme 3.72
CO
2
Me
(MeCN)
2
PdCl
2
, Cu(OAc)
2
R
CO
2
Me
N
S
O
O
N
S
O
O
N
N
R = H
3.185
3.186
Mg
MeOH
Zn, NH
4
Cl
CO
2
Me
CO
2
Me
H
H
3.187
3.188
Scheme 3.73
CO
2
Me
CO
2
Me
(MeCN)
2
PdCl
2
Cu(OAc)
2
N
S
N
S
N
N
O
O
3.189
3.190
O
O
Pd(OAc)
2
(1.2 eq)
PdX
N
S
N
N
N
3.192
O
2-PySO
2
SO
2
2-Py
O
3.191
Scheme 3.74
A related reaction using a ruthenium catalyst proceeded with reductive elimination to form a
carbon-hydrogen bond, giving the product of alkylation
3.184
, rather than alkenylation, with a saturated
side chain. This means that there was no net reduction, so no oxidant was needed (Scheme 3.72).
73
If the substrate does not possess an appropriate directing group, one may be attached by a temporary linker.
The 2-pyridyl sulfonyl group is a useful directing group for C-H activation. The pyrrole derivative
3.185
gave
the
-alkenylation product
3.186
. In the pyrrole series, an
N
-pyridyl sulfonyl group did not change the inherent
regioselectivity, which is naturally
, but did have a significant activating effect: the corresponding
N
-tosyl
derivative gave almost no product under the same conditions (Scheme 3.73).
74
Consistent with electrophilic
palladation, existing substituents exert a distinct effect on the reaction rate. Thus, the pyrrole derivative with
