Chemistry Reference
In-Depth Information
O
MCM-41-2P-Pd(0)
NEt
3
, CO (1 bar)
RT
I
23 examples
45-91%
R'
R'
R
R
Scheme 10.36
[MCM-41-2p-Pd(0)]-catalysed carbonylative Sonogashira coupling re-
action of aryl iodides.
O
Br
[(cinnamyl)PdCl]
2
(2 mol%)
BuPAd
2
,K
2
CO
3
, DMF, 100 °C
CO
18 examples
47 -88%
R"
R'
R'
R"
Scheme 10.37 Pd-catalysed carbonylative Sonogashira coupling of aryl bromides.
O
13 examples
50-83 %
OTf
[(c innam y l)PdC l]
2
(1 mol%)
Xantphos, toluene, NEt
3
,110 °C
CO
R"
R'
R'
R"
Scheme 10.38 Pd-catalysed carbonylative Sonogashira coupling of aryl triflates.
polymer-supported palladium catalyst.
46
Terminal alkynes were converted
with aryl iodides under 1 bar of CO to give alkynones in good to high yields
(Scheme 10.36). It is noteworthy that the use of a polymer as support in a
Sonogashira coupling reaction was earlier reported by Takahashi and co-
workers in 2008, where the products could be released from the polymer by
adding acid.
47
So far, basically all methodological developments in this area were fo-
cused on the use of expensive and easy-to-activate aryl iodides. It was
therefore interesting that in 2010 Beller and co-workers reported a general
and convenient palladium-catalysed carbonylative Sonogashira coupling of
aryl bromides.
48
Key to success was the application of BuPAd
2
as ligand in
the presence of K
2
CO
3
. Alkynones were generated in moderate to good yields
from the corresponding aryl bromides and terminal alkynes (Scheme 10.37).
The one-pot synthesis of isoxazolines and pyrazoles was also successful.
Since aryl triflates can be easily generated from the corresponding phe-
nols, in 2011 Beller's group developed a palladium-catalysed carbonylative
Sonogashira coupling of aryl triflates.
49a
This is the first carbonylative
Sonogashira protocol to apply aryl triflates as substrates. Various alkynones
were produced in moderate to good yields under a low pressure of CO
(Scheme 10.38). A one-pot synthesis of enaminones was also achieved by
running the reaction in the presence of primary amines. As arylamines are
abundantly available and relatively inexpensive, the authors also succeeded
in using amine as a precursor of electrophiles.
49b
In the presence of tBuONO
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