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Br
R
Pd-P-SiO
2
Ph
R
+
120 °C
PhSi(OMe)
3
Hiyama Coupling
Ph
Ph
Ph
N
Ph
S
Ph
Me
MeOOC
99%
99%
78%
43%
23%
Figure 13.21 Continuous flow Hiyama coupling using a silica-supported catalyst.
Br
R
SiliaCat DPP-Pd
R
R
+
60-80 °C
R
2
Zn or RZnBr
Negishi Coupling
O
NO
2
O
N
Me
N
O
OEt
O
2
N
OMe
83%
OHC
50%
81%
81%
Figure 13.22 Continuous flow Negishi coupling using a silica-supported catalyst.
continuous flow.
52
A silica-supported catalyst was loaded into a cartridge to
form a micro packed-bed reactor (Figure 13.22). A wide variety of different
substrates could be processed at 80 1C with a residence time of 5 min.
Notably, a single cartridge allowed 20 consecutive reactions to be executed
without a decrease in activity. Alternatively, a 4 h experiment could be per-
formed without a noticeable decrease in eciency. This resulted in a TON
higher than 120. Contamination of the desired compounds with palladium
was low (0.027 ppm Pd), suggesting a low leaching behavior of the immo-
bilized catalyst.
13.4.9 Decarboxylative Cross-Coupling in Flow
Decarboxylative cross-coupling is a new strategy to construct carbon-carbon
bonds. A copper co-catalyst is used to prepare the carbon nucleophile via a
protodecarboxylation reaction of arylcarboxylic acids. A continuous flow
strategy was developed to accelerate these reactions at 170 1C.
53
An im-
portant aspect of the study involved dealing with solubility issues, which
otherwise led to clogging of the microreactor. First, NMP was used to ensure
complete dissolution of all reagents. Second, aryl halides were replaced with
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