Chemistry Reference
In-Depth Information
O
15 examples
40-88%
PdCl
2
(PPh
3
)
2
(5 mol%
)
hv, NEt
3
, CO (45 bar)
C
6
H
6
/H
2
O
RI
R'
R
R'
Scheme 10.39 Pd-catalysed carbonylative Sonogashira coupling of
iodoalkanes
using xenon light.
PhCCH+Base
CO
OC
L
Pd
Base+H
X
Ph
X
Ph
Pd
L
CO
X
O
Ph
Pd
X
Ph
L
Pd
L
PhX
PhCCH+Base
O
Ph
Pd(0)
Pd
L
Ph
Ph
Base+HX
L
PhCOCCPh
PhCCPh
X=I,Br,Cl,OTf,etc
Scheme 10.40 Proposed reaction mechanism for the carbonylative Sonogashira
reaction (left) versus non-carbonylative Sonogashira reaction (right).
as oxidant and tri(2-furyl)phosphine as ligand, various arylamines were
coupled with terminal alkynes and gave the corresponding alkynones in
moderate to good yields.
Ryu and co-workers reported the synthesis of alkyl alkynyl ketones via Pd/
light-induced carbonylative Sonogashira coupling of iodoalkanes with
terminal alkynes.
50
Using xenon light, in the presence of a catalytic amount
of PdCl
2
(PPh
3
)
2
and NEt
3
, alkynones were produced in good yields
(Scheme 10.39). This represents the first example of Sonogashira carbony-
lations of iodoalkanes (alkyl iodides).
51
Despite all the synthetic developments to date, relatively little detailed
mechanistic work has been performed on Sonogashira carbonylations. The
generally accepted mechanism is shown in Scheme 10.40. The typical re-
action starts with the oxidative addition of ArX to a palladium(0) complex to
form an arylpalladium(II) intermediate. Subsequent insertion of CO leads to
the respective acyl-palladium complex. Transmetallation and finally re-
ductive elimination release the product and a new catalytic cycle can be
started. Notably, all species passing through the cycle are believed to be in a
reversible equilibrium.
Intramolecular Sonogashira carbonylations offer various possibilities for
the preparation of interesting heterocycles. Typically, in these reactions
2-halophenols and 2-haloanilines or their derivatives are employed with
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