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Pd(OAc)
2
(3 mol%)
IMes.HCl (6mol%)
CuI (2 mol%)
X
R
+
R
Me
3
Si
Ph
Ph
Cs
2
CO
3,
DMA, 80°C
0.25 -3 h
X=Br,Cl
OHC
Ph
MeO
Ph
Ph
X=Br,NoCuI
92%
X=Br
88%
X=Br
93%
Ph
Ph
X=Br
82%
X=Cl
51%
Scheme 4.39
Sila-Sonogashira reaction using an in situ-generated system.
N
NN
63
(1 mol%)
PPh
3
(1 mol%)
CuI (2 mol%)
O
X
R
I
Pd
I
R
+
H
R'
R'
Et
3
NorCs
2
CO
3
DMF, RT - 80°C
N
X=Br,I
N
63
Scheme 4.40 N-Carbamoyl-substituted Pd-NHC complexes for the Sonogashira re-
action using terminal alkynes.
catalytic amount of CuI to promote the reaction. Under these conditions, the
formation of the undesired dimerization product was not mentioned by the
authors.
In the following years, other protocols were developed and the main ad-
vances can be found in excellent reviews.
9d,136
In the following section, we
focus on the main developments after the award of the 2010 Nobel Prize in
Chemistry.
4.3.3.2 Alkynylation Reactions in Water
In 2010, Roy and Plenio reported on the preparation of sulfonated NHCs to
perform the coupling in water.
60
Since many protocols were already present in
the literature for the coupling of aryl bromides, the authors focused their
attention on the reactivity of pyridine and thiophene halides (Scheme 4.41).
The reaction involved an in situ-generated system consisting of Na
2
PdCl
4
(0.25
mol%) and ligand 64 (0.5 mol%). The reaction occurred in a 1 : 1 water-iPrOH
mixture at 90-95 1C using KOH as the base. Notably, the catalyst loading re-
ported was amongst the lowest at the time for reactions in water. Interestingly,
alkylacetylenes were also found to be suitable coupling partners.
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