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In-Depth Information
O
O
CO
2
Me
N
CO
2
Me
N
O
O
N
N
Boc
Boc
O
CO
2
Me
N
N
O
CO
2
H
O
O
N
(
t
-Bu
3
P)
2
Pd
Br
Boc
O
5
O
NH
CO
2
H
+
NMP, 93-99 °C
O
O
CO
2
Me
N
O
O
H
CO
2
H
N
Boc
~ 6 kg scale
H
N
O
CO
2
H
O
6
O
N
O
O
O
S
N
H
O
N
O
N
O
O
O
Scheme 3.12
(t-Bu
3
P)
2
Pd-catalyzed Heck reaction.
R
I
I
(Q
Phos)
2
Pd
−
R
n
toluene, 100 °C, 4-16 h
X
n
X
Scheme 3.13 L
2
Pd(0)-catalyzed carboiodination reaction.
demonstrated the use of (Q-Phos)
2
Pd in a novel carboiodination reaction
(Scheme 3.13).
57,58
Other L
2
Pd precatalysts gave lower yields of the product.
This process could be extended to a number of different substrates in order
to form various benzene-fused heterocycles.
59
Interestingly, in a few selected
cases (t-Bu
3
P)
2
Pd was found to be superior to (Q-Phos)
2
Pd.
60,61
Notably, in
the carboiodination reaction the LPd-based complex Q-PhosPd(crotyl)(Cl)
did not perform well. However, the addition of 1 mol % of Q-Phos ligand to
Q-PhosPd(crotyl)(Cl) resulted in very good conversion,
62
suggesting the
importance of a 2 : 1 ligand-to-Pd ratio to form L
2
Pd(0) for this reaction,
under these reaction conditions. An entire chapter is dedicated to this work
(see Chapter 7).
Lipshutz and co-workers recently demonstrated that the stereochemical
outcome of a coupling reaction depends largely on the nature of the ligand
employed.
63
A number of precatalysts, and also in situ-generated catalysts,
were evaluated in a Suzuki-Miyaura coupling of a (Z)-alkenyl halide with
arylboronic acids. Most of the L
2
Pd(0)-based precatalysts or the well-known
Suzuki-Miyaura coupling catalysts gave scrambling of the isomers, whereas
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