Chemistry Reference
In-Depth Information
11
(2 - 5 mol%)
RX
+
'
''
2
RR'
Conditions A - D
RT - 100°C
NN
sp
3
-sp
3
:
sp
2
-sp
3
:
Pd
Cl
N
O
NC
4
HN
OMe
N
OMe
X=Br,BR'
2
=9-BBN
A, RT: 81%
X = Cl, B R''
2
=9-BBN
B, RT: 100%
11
sp
3
-sp
2
:
sp
2
-sp
2
:
Me O
t
Bu
NN
S
N
N
OMe
O
X=Br,BR''
2
=B(OH)
2
C, 60°C: 83%
X=Cl,BR '
2
=BF
3
K
D, 100°C: 96%
X = Cl, BR''
2
=
D, 100°C: 86%
B
O
Conditions: A) K
3
PO
4
.H
2
O, dioxane; B ) K
3
PO
4,
THF/H
2
O; C) KO
t
Bu, dioxane/MeOH; D) K
3
PO
4,
dioxane/H
2
O
Scheme 4.6 Reactivity of 11 in the Suzuki reaction for the creation of various kinds
of bonds.
was then accomplished with moderate yields. A few years later, Organ and
co-workers used the well-defined [Pd(IPr)(PEPPSI)] complex (4 mol%) in
this reaction to form both sp
3
-sp
3
and sp
3
-sp
2
bonds.
41
The scope of the
reaction was considerably expanded and the desired compounds were ob-
tained in better yields. The reaction conditions were also milder (K
3
PO
4
as
the base, room temperature).
In 2010, Kantchev and co-workers explored the reactivity of various
[Pd(NHC)(palladacycle)] complexes in Suzuki-Miyaura cross-coupling.
42
Among several precatalysts, the IPr-cyclopalladated acetanilide complex 11
was found to be particularly active in the reaction due to its easy activation.
Interestingly, 11 allowed the formation of a wide range of C-C bonds in-
cluding sp
2
-sp
2
bonds but also sp
3
-sp
3
and sp
3
-sp
2
bonds (Scheme 4.6).
Another example of a challenging Suzuki-Miyaura reaction was reported
by Organ and co-workers in 2012.
43
[Pd(IPent)(PEPPSI)] (4) was used to
promote the coupling of allylboronic acids. The challenge in this kind of
coupling is to obtain good selectivities between a- and g-arylated products.
[Pd(IPent)(PEPPSI)] showed high selectivity (497%) for the formation of the
a-product and several aryl and heteroaryl halides were successively coupled
in the presence of 5 M KOH in THF (Scheme 4.7).
4.3.1.1.3 Asymmetric Suzuki Coupling. In a rare example of an asym-
metric Suzuki reaction, Labande and co-workers prepared a range of new
palladium complexes bearing chiral phosphine-NHC ligands with planar
chirality (12, Figure 4.8).
44
These complexes were then used to prepare
chiral binaphthyl compounds. Good yields and moderate enantioselec-
tivities were obtained (ee up to 42%, Scheme 4.8), using low catalyst load-
ings (0.1-0.5 mol%).
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