Oxalyl chloride as carbonyl synthon in Pd-catalyzed carbonylations of triarylbismuth and triarylindium organometallic nucleophiles

Article abstract of DOI:10.1016/j.tetlet.2010.07.074

Oxalyl chloride has been demonstrated to function as C1 carbonyl synthon in the carbonylations of triarylbismuth and triarylindium nucleophiles under palladium-catalyzed conditions. All the three aryl groups from both bismuth and indium reagents participated in carbonylative couplings to afford the corresponding functionalized ketones in high yields. This study also disclosed a novel utilization of oxalyl chloride as facile alternative source of CO for carbonylations under palladium catalysis.

Full text of DOI:10.1016/j.tetlet.2010.07.074

Tetrahedron Letters 51 (2010) 4975–4980
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Tetrahedron Letters
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Oxalyl chloride as carbonyl synthon in Pd-catalyzed carbonylations
of triarylbismuth and triarylindium organometallic nucleophiles
*
Maddali L. N. Rao , Varadhachari Venkatesh, Priyabrata Dasgupta
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Oxalyl chloride has been demonstrated to function as C1 carbonyl synthon in the carbonylations of tri-
arylbismuth and triarylindium nucleophiles under palladium-catalyzed conditions. All the three aryl
groups from both bismuth and indium reagents participated in carbonylative couplings to afford the cor-
responding functionalized ketones in high yields. This study also disclosed a novel utilization of oxalyl
chloride as facile alternative source of CO for carbonylations under palladium catalysis.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 23 May 2010
Revised 7 July 2010
Accepted 13 July 2010
Available online 17 July 2010
Keywords:
Oxalyl chloride
Carbonylations
C1 synthon
Triarylbismuths
Triarylindiums
Palladium
Atom-efficient
Development of new processes involving small molecules is a
priority area of research in synthetic organic chemistry.1,2 Carbon-
ylation under metal-catalyzed conditions is a useful synthetic pro-
cess widely used in industry as it provides an easy access to
carbonyl compounds.3 However, there are some inevitable prob-
lems associated in the utilization of CO gas for carbonylations from
safety and other related issues.3,4 This had led to the use of alterna-
tive carbonyl sources such as formates, formamides, chloroform,
aldehydes, and metal carbonyls, as carbonyl synthons for various
synthetic transformations in place of gaseous CO.4
In this context, oxalyl chloride needs a special mention. This has
been known to be involved as C1 or C2 synthon in synthetic organ-
ic chemistry for ketone synthesis.5,6 Notably, its use as C1 synthon
under metal catalysis has not evolved so far for synthetic applica-
tions. For instance, oxalyl chloride as C1 synthon was reported in
1,1-cycloaddition reactions with dialkenyl metal compounds.5 As
C2 synthon6 this has been utilized in combination with organome-
tallic (Li, Mg, and Cu) reagents and in Friedel–Crafts reaction. Given
the importance of carbonylations in pharmaceutical and industrial
applications,3 there is a genuine need for facile reactive alternate
carbonyl synthons7 for safer execution of these processes.4
simplicity, facile reactivity, and associated convenience in the uti-
lization of oxalyl chloride as carbonyl synthon under metal
catalysis.
With the recent interest in the use of organobismuth8 reagents
for C–C bond formations,8,9 we have elaborated the scope of acyl
chloride reactions with triarylbismuths10 involving non-decarb-
onylative couplings to give unsymmetrical ketones in the pres-
ence of palladium catalysts.11 Driven by this, it was of interest
to study these reactions with oxalyl chloride for new synthetic
applications. To our astonishment, the reaction of oxalyl chloride
with triphenylbismuth in the presence of palladium catalyst pro-
duced benzophenone (1) as a product (Table 1, entry 1). The forma-
tion of ketone and not a diketone6a as product indicated the
participation of oxalyl chloride as C1 carbonyl synthon in this reac-
tion. A brief literature survey revealed the Stille’s observation in
1979 on the formation of acetone as product (10% yield) in the
reaction of oxalyl chloride with tetramethyltin under palladium
catalysis.12 However, there are no reports afterwards on further
utilization of oxalyl chloride in this direction. This made us to
explore the potential use of oxalyl chloride as C1 carbonyl synthon
in the carbonylative couplings with additional screening under
various conditions (Table 1).
In this direction, we describe here a novel carbonylations using
oxalyl chloride as C1 carbonyl synthon under palladium-catalyzed
conditions. These results are significant from the view point of its
The coupling reactions carried out under different palladium
conditions furnished the carbonylation product benzophenone
(1) in lower amounts (entries 1–3). Further, it was revealed to us
that the carbonylation process is more effective without NEt3 (en-
tries 4 and 5).13 The reaction carried out with 1 equiv of oxalyl
* Corresponding author. Tel./fax: +91 512 2597532.
E-mail address: maddali@iitk.ac.in (M.L.N. Rao).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.07.074

4976
M. L. N. Rao et al. / Tetrahedron Letters 51 (2010) 4975–4980
Table 1
Screening with BiPh3
chloride provided only moderate yield of ketone (entry 6). This
a–d
may be due to insufficient amount of oxalyl chloride (1 equiv) used
in the reaction to carbonylate 3 equiv of phenyl groups from tri-
phenylbismuth reagent. So, further study was carried out with
2 equiv of oxalyl chloride. The screening carried out with different
solvents, catalysts, and temperature conditions (entries 7–11) re-
vealed that 2 equiv of oxalyl chloride at 80 °C in 1,4-dioxane is
optimal to obtain high yield of ketone (entry 5). A control reaction
without catalyst provided very poor yield of the carbonylation
product (entry 12). Another reaction without oxalyl chloride under
these conditions furnished homo-coupled biphenyl as a product
from triphenylbismuth reagent.10
So, to expand the scope of this carbonylation, further studies
have been carried out with divergently functionalized BiAr3 re-
agents under the established coupling conditions14 (Table 2). These
reactions involving different triarylbismuth reagents reacted in a
facile manner in the carbonylative couplings to furnish high yields
of the corresponding functionalized ketones. It is noteworthy that
both electron-rich and electron-deficient triarylbismuth com-
pounds fared well to give various functionalized ketones under
the established protocol.
[Pd]
(COCl)2
BiPh3
PhCOPh
+
1
( )
Entry
Catalyst
Solvent
Temp (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
PdCl2/2PPh3
Pd(PPh3)4
PdCl2/2PPh3
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
PdCl2(PhCN)2
Pd(PPh3)4
—
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
DME
CH3CN
THF
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
80
rt
rt
4
12
12
4
4
4
4
4
4
4
38e
À(35)e
À(32)e
79f
80
80
80
80
80
80
80
rt
89g
49h
78
80
47
51
48
10
11
12
4
4
80
À(20)
a
b
c
Pd catalyst (0.09 equiv), BiPh3 (1 equiv), (COCl)2 (2 equiv), solvent (3 mL).
Isolated yields are given.
GC conversions are given in parenthesis.
Biphenyl as minor side product formed in these reactions.
Condition: Pd catalyst (0.15 equiv), PPh3 (0.30 equiv), BiPh3 (1 equiv), COCl2
d
e
Encouraged by these novel carbonylative couplings of triaryl-
bismuths with oxalyl chloride, the corresponding carbonylation
studies using arylindium reagents are of interest as these com-
pounds showed facile reactivity under CO conditions.15a,15b
(2 equiv), Et3N (5 equiv)
f
With Et3N (2 equiv).
g
Without Et3N.
h
With (COCl)2 (1 equiv).
Table 2
Carbonylations of triarylbimuthsa–d
O
Ar
Ar
(COCl)2 (2 equiv)
[Pd]
Bi
Ar
Ar
Ar
(1 equiv)
(1.5 equiv)
Entry
1
Triarylbismuth
Ketone
Yield (%)
89
O
Bi
3
1
O
O
Bi
Me
2
80
3
2
Me
Me
Me
Me
Bi
Bi
Bi
3
4
76
70
3
3
3
Me
O
F3C
CF3
4
CF3
O
F
5
86
3
5
F
F
O
Bi
Bi
Cl
3
6
7
82
80
3
6
Cl
Cl
Cl
Cl
O
7
Cl

M. L. N. Rao et al. / Tetrahedron Letters 51 (2010) 4975–4980
4977
Table 2 (continued)
Entry
Triarylbismuth
Ketone
Yield (%)
O
Bi
MeO
OMe
8
9
77
84
3
OMe
8
O
Bi
Bi
Bi
Bi
Bi
Bi
Bi
OMe
3
9
MeO
OMe
O
OEt
10
11
12
13
14
82
76
78
75
79
72
3
10
O
O
O
Oi-Pr
3
11
Oi-Pr
i-PrO
O
O
n-Bu
3
3
12
n-BuO
i-BuO
s-BuO
On-Bu
O
Oi-Bu
13
Oi-Bu
O
O
s-Bu
3
14
Os-Bu
O
Oallyl
15
3
15
O
O
a
Conditions: Pd(PPh3)4 (0.09 equiv), BiAr3 (1 equiv), (COCl)2 (2 equiv), 1,4-dioxane (3 mL), 80 °C, 4 h.
Isolated yields are given.
b
c
Biaryls as minor side product formed in some reactions.
d
All the ketone products were characterized by 1H NMR, 13C NMR, IR, and HRMS analyses.
Table 3
Screening with InPh3
carbonylation product (entry 7). Without oxalyl chloride under
these conditions the reaction gave homo-coupled biphenyl as a
product from triphenylindium reagent.
a–d
With the optimum condition in hand for the carbonylation of
indium reagents, we elaborated the study with different triarylin-
dium reagents16,17 (Table 4). The reactions using different triarylin-
diums showed excellent reactivity in carbonylative couplings
leading to the corresponding functionalized aromatic ketones in
high yields. The coupling reactivity of both triarylbismuths and tri-
arylindiums was found to be almost similar under the conditions
studied. Thus the present process served as a novel carbonylation
procedure using oxalyl chloride. This is a first successful demon-
stration of oxalyl chloride to serve as a C1 carbonyl synthon under
[Pd]
(COCl)2
InPh3
PhCOPh
+
(1)
Entry
Catalyst
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Temp (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
rt
4
4
1
3
4
4
4
38
54
58
76
40
60
60
60
60
60
83
PdCl2(PhCN)2
—
À(16)
À(4)
palladium catalysis and is
a long wait after Stille’s initial
a
observation.12
Conditions: Pd catalyst (0.09 equiv), InPh3 (1 equiv), (COCl)2 (2 equiv), THF
(5 mL).
It is to be mentioned that carbonylative cross-coupling of orga-
nometallic reagents with organic electrophiles is a known route for
the synthesis of ketones.18 However, the corresponding carbonyla-
tive homo-coupling to give ketones is somewhat difficult in terms
of reactivity and selectivity.19
b
Isolated yields are given.
c
GC conversions are given in parenthesis.
Biphenyl as minor side product formed in these reactions.
d
A brief screening of triphenylindium with oxalyl chloride was
carried out as given in Table 3. The carbonylations using in
For example, the rhodium- or palladium-catalyzed carbonyla-
tions of triarylbismuths led to the formation of either ketone or es-
ter products depending on the conditions employed with
atmospheric pressure of CO.19a,19b However, in this study it was
also mentioned that the carbonylative couplings of triarylbismuths
with CO were found to be ineffective with complexes such as
15c
situ-generated InPh3
offered moderate yield of benzophenone
(1) at lower temperature conditions (entries 1 and 2). Further
screening revealed Pd(PPh3)4 in THF solvent at 60 °C for 4 h (entry
5) as effective condition for carbonylation (entries 3–6). A control
reaction without catalyst produced very poor amount of the

4978
M. L. N. Rao et al. / Tetrahedron Letters 51 (2010) 4975–4980
Pd(PPh3)4, PdCl2(PPh3)2, and Pd(CO)(PPh3)3 to give ketone prod-
ucts.19b Whereas the present method with Pd(PPh3)4 catalyst is
effective for carbonylations of both triarylbismuths and triarylindi-
ums using oxalyl chloride as carbonylating agent. Thus, the meth-
od described is uniquely advantageous as oxalyl chloride is serving
as C1 synthon in a novel decarbonylative carbonylation process in
the presence of palladium catalyst.
To understand the carbonylation process, we have carried out
some cross-over experiments with the combination of two differ-
ent triarylbismuths as given in Scheme 1. The product distribution
Table 4
Carbonylations of triaryindiumsa–d
O
Ar
Ar
(COCl)2 (2 equiv)
[Pd]
In
Ar
Ar
Ar
(1 equiv)
(1.5 equiv)
Entry
1
Triarylbismuth
Ketone
Yield (%)
83
O
In
3
1
O
O
In
Me
2
71
3
2
Me
Me
Me
Me
In
In
In
3
4
74
69
3
3
3
Me
O
F3C
CF3
4
CF3
O
F
5
6
79
71
3
5
F
F
O
In
Cl
3
6
Cl
Cl
Cl
Cl
O
In
In
In
7
8
70
76
3
3
7
Cl
O
O
MeO
OMe
8
OMe
OMe
9
10
11
12
13
79
70
68
67
68
3
9
MeO
OMe
O
In
In
In
In
OEt
3
10
O
O
O
Oi-Pr
3
11
Oi-Pr
i-PrO
n-BuO
i-BuO
O
On-Bu
Oi-Bu
3
12
On-Bu
O
3
13
Oi-Bu

M. L. N. Rao et al. / Tetrahedron Letters 51 (2010) 4975–4980
4979
Table 4 (continued)
Entry
Triarylbismuth
Ketone
Yield (%)
O
In
Os-Bu
14
71
70
3
14
Os-Bu
s-BuO
O
In
Oallyl
15
3
15
O
O
a
Condition for InAr3: Pd(PPh3)4 (0.09 equiv), InAr3 (1 equiv), (COCl)2 (2 equiv), THF (5 mL), 60 °C, 4 h.
Isolated yields are given.
b
c
Biaryls as minor side product formed in some reactions.
d
All the ketone products were characterized by 1H NMR, 13C NMR, IR, and HRMS analyses.
based on GC–MS analysis is given. In general, these experiments
mation of B via transmetalation of A with Ar-M followed by
decarbonylation cannot be ruled out at this stage.
revealed the formation of unsymmetrical ketones derived from
two different triarylbismuths along with symmetrical ketones di-
rectly from single triarylbismuth reagent. However, the formation
of minor amounts (<2%) of homo-coupled biaryls was also ob-
served in (i) and (iii) reactions (Scheme 1).10 Hence, these cross-
over experiments indicated: (i) the relative propensity of the aryl
group transfer from different Ar-Bi species to give mixed ketones;
(ii) the participation of three aryl groups from triarylbismuths in
carbonylative couplings; (iii) the involvement of two different
Ar-Bi species in the catalytic cycle to give mixed ketones. Impor-
tantly, similar trend of formation of mixed ketones was observed
by Seyferth and Spohn in the carbonylations of organomercurials
using metal carbonyls.20
Based on the above observations, the catalytic cycle proposed
for carbonylative couplings is given in Scheme 2. The initial oxida-
tive addition of oxalyl chloride to Pd(0) would give intermediate, A.
This upon decarbonylation21 followed by transmetalation with Ar-
M (M = Bi, In) generates intermediate, B. This may undergo acyl
migration and second transmetalation to give diorganylpalladium
D via the intermediate C. Reductive elimination of intermediate
D is expected to deliver the ketone product. The formation of
mixed ketones in cross-over experiments supports two time
involvement of Ar-Bi species during catalytic cycle. Alternate for-
In summary, we have demonstrated the use of oxalyl chloride
as C1 carbonyl synthon in the carbonylation of triarylbismuth
and triarylindium nucleophiles under palladium-catalyzed condi-
tions. This is a novel protocol involving oxalyl chloride as facile
alternative source of CO for carbonylations under palladium catal-
ysis. In addition all the three aryl groups from both bismuth and
indium reagents participated in carbonylative couplings to afford
functionalized ketones in high yields. Given the need for the use
of alternative carbonylating agents in metal-catalyzed carbonyla-
tions,4 this study is expected to have immense synthetic potential
in that direction. As the synthetic reactions using oxalyl chloride
under metal catalysis are scarce, the present method would open
up a plethora of opportunities in the use of oxalyl chloride as C1
carbonyl synthon for various synthetic applications.
Acknowledgments
We thank the Department of Science and Technology (DST), In-
dia for supporting this work under green chemistry program (SR/
S5/GC-11/2008). V.V. and P. D. thank UGC, New Delhi, and CSIR,
New Delhi, for research fellowships, respectively.
Supplementary data
[Pd]
Bi(Ar1)3
Bi(Ar2)3
Ar1CAr1 Ar1CAr2 Ar2CAr2
+
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.07.074.
+
+
(COCl)2
(4 equiv)
O
O
O
(1 equiv)
(1 equiv)
Ar1 = Ph, Ar2 = 4-Me-Ph
27%
20%
26%
51%
57%
53%
18%
23%
19%
(i)
References and notes
(ii) Ar1 = Ph, Ar2 = 3-OMe-Ph
(iii) Ar1 = Ph, Ar2 = 4-F-Ph
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Scheme 1. Cross-over experiments. Reagents and conditions: (a) Pd(PPh3)4
(0.18 equiv), BiAr3 (1 equiv) and BiAr3 (1 equiv), (COCl)2 (4 equiv), 1,4-dioxane
(6 mL), 80 °C, 4 h; (b) GC–MS ratios are given.
1
2
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O
(COCl)2
ArCOAr
Cl Pd
Pd(0)
COCl
A
)
(
reductive
oxidative
elimination
addition
- CO
Ar COPd Ar
M = Bi, In
D
)
(
ClPdCOCl
MAr3
Ar2MCl
acyl
migration
trans-
trans-
metalation
ArCOPdCl
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(B)
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Scheme 2. Proposed catalytic cycle.

4980
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gun under high vacuum for 0.5 h. Once it was completely dried, the flask was
filled with nitrogen and re-evacuated. Then THF (5 mL) was added through a
syringe. To this, ArMgBr (1.62 mmol) was added dropwise via a pressure-
equalizing funnel for about 1 h. The contents of the flask were allowed to stir
for 0.5 h. The resultant triarylindium solution was directly used for
carbonylation reactions using oxalyl chloride.
17. General procedure for the carbonylations of InAr3 with oxalyl chloride: A 50-
mL oven-dried Schlenk tube was charged with InAr3 (0.5 mmol) in THF solvent.
To this, Pd(PPh3)4 (0.045 mmol) catalyst was added followed by oxalyl chloride
(1.0 mmol). The contents were stirred at 60 °C for 4 h. After the reaction, THF
solvent was removed under vacuum. The residue was treated with water and
extracted with ethyl acetate (25 mL Â 1). The organic extract was washed with
10% HCl (5 mL Â 1), brine (5 mL Â 2), dried over anhydrous MgSO4, and
concentrated. The crude material was purified by column chromatography
(SiO2 60–120, ethyl acetate/petroleum ether as an eluent) to obtain the pure
ketone product. All the ketone products were characterized by 1H NMR, 13C
NMR, IR, and HRMS studies.
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an additive (Ref. 11).
14. General procedure for the carbonylations of BiAr3 with oxalyl chloride: A 50-
mL oven-dried Schlenk tube was charged with BiAr3 (0.5 mmol), Pd(PPh3)4
(0.045 mmol), and anhydrous 1,4-dioxane (3 mL) under nitrogen atmosphere.
Then oxalyl chloride (1.0 mmol) was added and the contents were stirred at
80 °C for 4 h. After the reaction time, 1,4-dioxane was removed under vacuum.
The residue was treated with water and extracted with ethyl acetate
(25 mL Â 1). The organic extract was washed with 10% HCl (5 mL Â 1), brine
(5 mL Â 2), dried over anhydrous MgSO4, and concentrated. The crude material
was purified by column chromatography (SiO2 60–120, ethyl acetate/
petroleum ether as an eluent) to obtain the pure ketone product. All the
ketone products were characterized by 1H NMR, 13C NMR, IR, and HRMS
studies.
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16. The InAr3 reagents used for carbonylation studies were prepared by following
the reported procedure.15c Indium(III) chloride (0.5 mmol, 0.1105 g) was
placed in a round-bottomed flask with a stirring bar and heated with a heat
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Chem. 1996, 61, 9082–9083.
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