Pd/C-catalyzed synthesis of oxamates by oxidative cross double carbonylation of amines and alcohols under Co-catalyst, base, dehydrating agent, and ligand-free conditions

Article abstract of DOI:10.1021/jo401038e

This work reports a mild, efficient, and ligand-free Pd/C-catalyzed protocol for the oxidative cross double carbonylation of amines and alcohols. Notably, the reaction does not requires any base, co-catalyst, dehydrating agent, or ligand. Pd/C solves the problem of catalyst recovery, and the catalyst was recycled up to six times.

Full text of DOI:10.1021/jo401038e

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Note
Pd/C catalysed synthesis of oxamates by oxidative cross
double carbonylation of amines and alcohols under co-
catalyst, base, dehydrating agent and ligand-free conditions
Sandip T. Gadge, and Bhalchandra M. Bhanage
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo401038e • Publication Date (Web): 05 Jun 2013
Downloaded from http://pubs.acs.org on June 5, 2013
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Pd/C catalysed synthesis of oxamates by oxidative cross double carbonylation of amines and
alcohols under co-catalyst, base, dehydrating agent and ligand-free conditions
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Sandip T. Gadgea and Bhalchandra M. Bhanagea*
a Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga,
Mumbai-400019. India. Fax: +912222692102
bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in
Abstract
This work reports, a mild, efficient and ligand-free Pd/C catalysed protocol for the oxidative
cross double carbonylation of amines and alcohols has been developed. Notably, the reaction does
not requires any base, co-catalyst, dehydrating agent or ligand. Pd/C solves the problem of catalyst
recovery, and the catalyst was recycled up to six times.
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Oxamates are important functional moieties in the synthesis of numerous organic
molecules, biologically active compounds, and natural products.1 For the synthesis of oxamates
various methods such as acylation of the appropriate amine with mono esters of oxalyl chloride1 or
diester of oxalic acid are reported.2 These methods are stoichiometric and requires the use mono
esters of oxalyl chlorides which are thermally unstable.3 In addition to this, synthesis of mono
esters of oxalyl chlorides require the combination of equimolar quantities of oxalyl chloride and the
appropriate alcohol with distillation setup for isolation of product from reaction mixture.3
Murahashi et al. reported an alternative route for the synthesis of oxamates by carbonylation of
amines and alcohols using stoichiometric amount of homogeneous PdC12(MeCN)2 catalyst system
and a mixture of carbon monoxide and oxygen (CO/O2, 80:5 kg/cm2). They used CuI as a co-
catalyst, dehydrating agent such as trimethoxy methane and triethyl amine as a base.4 The major
drawbacks associated with this method are: the use of homogeneous catalyst system along with CuI
as co-catalyst, dehydrating agent, high pressure of CO/O2, reaction time up to 20 hours, limited
substrate scope, difficulty in separation of catalyst from product and its reuse. The method for
overcoming these drawbacks would involve the use of a heterogeneous palladium catalyst,
especially palladium on carbon (Pd/C), which has recently been investigated in a variety of organic
chemical fields from sustainable and industrial standpoints due to their easy access, recoverability,
reusability, low cost and avoidance of residual metals in the desired products.5 Based on our
research interest in carbonylation reactions 6, we had reported Pd/C as a ligand-free, heterogeneous
catalyst system which worked efficiently for the various carbonylation reactions.7
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In this paper, we describe an efficient and heterogeneous, ligand-free protocol for Pd/C-
catalyzed synthesis of oxamates using oxidative cross double carbonylation of amine and alcohol
(Scheme 1). This method avoids use of the base, ligand, co-catalyst, dehydrating agent, lower
reaction time with ease of recovery of Pd/C from the reaction mixture by the simple filtration.
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Present protocol tolerated a wide range of functional groups, applicable for varieties of substrates
such as allylic, benzylic, aliphatic, cyclic, heterocyclic symmetrical and unsymmetrical amines,
providing good to excellent yield of desired products.
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Scheme 1. Pd/C catalyzed oxidative cross double carbonylation of amines and alcohols.
We examined the effect of the 10% Pd/C catalyst using piperidine 1a and ethanol 2a as
substrates in the presence of CO/O2 (6:1 atm) for the present cross double carbonylation reaction
(Table 1). The catalyst loading could be increased to 8 mol% with significant increase in the yield
of the product (Table 1, entry 4). While reducing the catalyst loading results in lower yields of the
product.
Table 1. Effect of dose of Pd/C on the reaction. a
Entry
Catalyst
Catalyst loading
(mol%)
Yield
[%]b
1
2
3
4
5
78
57
81
98
99
5% Pd/C
8
4
10% Pd/C
10% Pd/C
10% Pd/C
10% Pd/C
6
8
10
a Reaction conditions: 1a (1 mmol), 2a (10 mL), TBAI (0.2
mmol), CO/O2 (6:1 atm), Temperature 60oC, Time 2 h. b GC
yield.
We then investigated the solvent effect on oxidative cross double carbonylation reaction.
The reaction hardly took place in THF, 1,4-dioxane or toluene using equimolar quantities of 1a and
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2a (Table 2 entries 1-3). The nature of solvent such as protic/aprotic is important for the Pd/C
catalysed oxidative carbonylation reaction.8a The activity of catalyst was found to be significantly
higher in polar solvents such as ethanol. The desired product was obtained in excellent yields
directly using ethanol as solvent (Table 2, entry 4).
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Table 2. Optimization of the Pd/C-catalyzed oxidative cross double carbonylation reaction.a
Entry Solvent
Effect of solvent
Additive
(mmol)
Temp
(oC)
Time Yield
[h]
[% ]b
1
2
3
4
THF
TBAI
60
60
60
60
2
2
2
2
20
1,4-dioxane TBAI
Toluene
EtOH
18
07
98
TBAI
TBAI
Effect of additive
5
6
7
EtOH
EtOH
EtOH
NaI
KI
----
60
60
60
2
2
2
93
91
----
Effect of temperature
8
9
EtOH
EtOH
TBAI
TBAI
50
70
2
2
79
99
Effect of time
10
11
EtOH
EtOH
TBAI
TBAI
60
60
1
3
79
98
a Reaction conditions: 1a (1 mmol), 2a (10 mL), 10% Pd/C (8
mol%), TBAI (0.2 mmol), CO/O2 (6:1 atm), Temperature 60oC,
Time 2 h. b GC yields.
Pd/C catalyst together with molecular oxygen and iodide additive plays a vital role in
oxidative carbonylation reactions.7a,b,8 The use of KI, NaI and tetrabutylammoniumiodide (TBAI)
was found to be specifically effective iodide additive (Table 2, entries 5 and 6), while with TBAI
excellent yield of the desired products was obtained (Table 2, entry 4). The reaction never
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proceeded without iodide source (Table 2, entry 7). The iodide has ‘softer’ binding nature, so it can
be easily adsorbs and desorbs from the catalyst surface.7b,8a The temperature of the reaction was
also important for the effective progress of the Pd/C-catalyzed cross double carbonylation reaction
(Table 2, entries 8 and 9). 60oC was found to be the optimum temperature and the target compound
3a was obtained with 98% yield in 2 hours (Table 2, entry 4). Further increase in temperature and
time has no profound effect on the yield of the product observed (Table 1, entries 9-11).
Thus, the optimized reaction conditions are: 1a (1 mmol), 2a (10 mL), Pd/C (8 mol%),
TBAI (0.2 mmol), CO/O2 (6/1 atm) at 60oC, for a time period of 2 hours.
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In order to study the potential and general applicability of developed methodology, various
amines containing different functional groups were investigated (Table 3). Cyclic secondary
amines such as piperidine, piperidine-4-carbonitrile, pyrollidine, and morpholine 1a-d were cross
double carbonylated with ethanol to give desired oxamates derivatives 3a-d in excellent yield
(Table 3, entries 1-4). Piperazine possessing either an electron withdrawing (fluoro group) or an
electron-donating functionality (methyl), were found to be good substrates for cross double
carbonylation and was not reported earlier. N-phenyl-, N-methyl-, N-benzyl- and 1-(2-
fluorophenyl)piperazine 1e-h underwent oxidative double carbonylation efficiently with ethanol to
afford corresponding oxamates 3e–h with high yields (Table 3, entries 5-8). As shown in Table 2,
the diallyl amine 1i as well as dibenzyl amine 1j showed excellent reactivity and selectivity and
provides 92% and 93% yield of desired product respectively (Table 3, entries 9 and 10). Double
carbonylation of secondary aliphatic amines such as diethylamine and dibutylamine 1k-l with
ethanol provided the product 3k-l in good yield (Table 3, entries 11 and 12).
The unsymmetrical amines, such as N-methyl-1-phenylmethanamine, 1,2,3,4-
tetrahydroisoquinoline and N-isopropylmethylamine 1m-o were also smoothly underwent coupling
reaction which gave excellent yields (Table 3, entries 13-15). The compounds 3h, 3j, 3m and 3o
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were obtained as 1/1 mixture of E/Z rotamers around the amide bond as shown by 1H and 13C NMR
spectra, while compound 3n showed mostly 2/1 mixture of E/Z rotamers around the amide bond.
No homo double carbonylation product, such as oxamide and oxalate, or cross single carbonylation
Table 3. Pd/C catalysed oxidative cross double carbonylation of amines and alcohols.a
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Entry
Amine
Alcohol
Product
Yield
[%]b
O
O
N
1
2
97
95
O
3a
2a
3
4
5
93
94
91
2a
2a
2a
6
7
95
89
2a
2a
8
9
87
92
2a
2a
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2a
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2a
2a
N
H
13
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16
88
90
94
93
2a
2a
2a
1m
1a
1a
17
94
a Reaction conditions: amine (1 mmol), alcohol (10 mL), 10% Pd/C (8 mol%), TBAI (0.2
mmol), CO/O2 (6:1 atm), Temperature 60oC, Time 2 h. b Isolated yields.
product, could be detected among the products. With primary amines, we observed the formation of
carbamate as a major product under such reaction condition.
Next, we examined the scope of Pd/C catalysed oxidative double carbonylation of piperidine
with various alcohols. Like ethanol, methanol 2b and n-butanol 2c furnished excellent yield of the
corresponding product 3p-q (Table 3, entries 16 and 17).
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The reusability of Pd/C is a great advantage in the decreasing environmental pollution and cost
reduction in process chemistry. We examined the reuse of Pd/C in the double carbonylation using
piperidine and ethanol as substrates in the presence of CO/O2 (6:1) at 60oC temperature (Table 4).
Pd/C could be reused successfully until the sixth run without either significant loss of yield or
extension of the reaction time. We also performed the reaction on larger scale (5 mmol of
piperidine) and leaching of palladium metal was investigated after the 1st and 6th recycle runs.
Table 4. Investigation in the reuse of Pd/C.
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Entry
Run
Yield
[%]a
97
1
2
3
4
5
6
1
2
3
4
5
6
97
96
95
94
93
aYields were determined by GC analysis.
Pd metal was not detected within the limits of the assay (<1 ppm) by analysis with inductively
coupled plasma atomic emission spectrometry (ICP-AES).
In conclusion, we have developed a facile, efficient, and environmentally friendly process
with widespread application for the synthesis varieties of oxamate derivatives using Pd/C as a
heterogeneous catalyst under ligand-free and mild conditions. Simple starting materials, less
reaction time, low pressure of CO/O2, avoid use of any base, co-catalyst and dehydrating agent
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adds an additional credit to the present study. The presented reaction demonstrates straightforward
Pd/C recovery and its successful reuse until the sixth run without loss in activity and selectivity.
The protocol would be practical for use as an economical synthetic method and offer an alternative
synthetic strategy for the practical construction of oxamate derivatives.
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Experimental Section
General: The Pd/C was purchased from Sigma-Aldrich (10 wt. % loading, matrix: activated carbon
support, Product Number: 205699, Brand: Aldrich). Product was purified by column
chromatography on silica gel (100-200) mesh. The product was visualized with a 254 nm UV lamp.
The IR spectra were recorded with FT-IR. The H and 13C NMR spectra were recorded with
1
300MHz and 400 MHz FT-NMR spectrometer in CDCl3. HRMS was recorded on a commercial
apparatus (ESI Source: ion trap). The chemical shifts are reported in parts per million (δ) relative to
tetramethylsilane as an internal standard. J (coupling constant) were reported in Hz, splitting
patterns of proton are described as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet). The
conformation of known compounds done by comparison with authentic samples on GC and GC-
MS. However new compounds were confirmed by GC-MS, FT-IR, H, 13C NMR and HR-MS
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techniques.
General experimental procedure for oxidative cross double carbonylation of amines and
alcohols:
Amine (1 mmol), alcohol (10 mL), 10% Pd/C (8 mol%), and TBAI (0.2 mmol) were added
to a 100-mL stainless steel autoclave, and the autoclave was closed, pressurised with oxygen (1
atm) and CO (6 atm) without flushing. The reaction mixture was stirred with mechanical stirred
(525 rpm) at 60oC temperature for two hours. After cooling it to room temperature, the pressure
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carefully released. The reactor vessel washed with ethyl acetate (3×5 mL) to remove traces of
product and catalyst if present. The filtrate was washed with saturated solution of sodium
thiosulphate (3×5 mL), dried over Na2SO4, and concentrated in vacuo. The residue was purified by
column chromatography (silica gel 100-200 mesh, petroleum ether/ ethyl acetate) to give the
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corresponding oxamate compounds. The compounds were confirmed by GC, GC-MS, FT-IR, H,
13C NMR, and HR-MS techniques.
Typical Procedure for Reuse of Pd/C:
After the reaction mixture was passed through a filter paper, crude Pd/C was washed with distilled
water (5 × 2.5 mL), methanol (5 × 2.5 mL) to remove trace amounts of organic material if present.
The resulting Pd/C was dried in vacuo, and used for catalyst recyclability experiment.
(3b) ethyl 2-(4-cyanopiperidin-1-yl)-2-oxoacetate
Yellowish liquid; 199 mg, yield- 95%; IR (Neat): 2242, 1729, 1666 cm–1; H NMR (400 MHz,
1
CDCl3): δ 4.35 (q, J= 7.16Hz, 2H), 3.79-3.67 (m, 2H), 3.64-3.58 (m, 1H), 3,47-3.40 (m, 1H), 3.00-
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2.94 (m, 1H), 2.03-1.91 (m, 4H), 1.37 (t, J= 7.16Hz, 3H); C NMR (75 MHz, CDCl3): δ 162.5,
160.1, 120.3, 62.4, 44.1, 39.2, 28.8, 27.8, 26.2, 14.0; GCMS (EI, 70 eV): m/z (%): 210 (14, M+),
181 (9), 137 (100), 109 (12), 94 (20), 67 (29), 56 (35), 42 (21); HRMS (ESI- ion trap): m/z= Calcd
for [(C10H14O3N2)Na]+: 233.0897, found: 233.0898.
(3e) ethyl 2-oxo-2-(4-phenylpiperazin-1-yl)acetate
Yellowish liquid; 238 mg, yield- 91%; IR (Neat): 1738, 1668 cm–1; 1H NMR (400 MHz, CDCl3): δ
7.31-7.26 (m, 2H), 6.94-6.91 (m, 3H), 4.36 (q, J= 7.16Hz, 2H), 3.80 (t, J= 5.12Hz, 2H), 3.61 (t, J=
5Hz, 2H), 3.22 (t, 4H), 1.40 (t, J= 7.16Hz, 3H); 13C NMR (75 MHz, CDCl3): δ 162.6, 160.1, 150.7,
129.3, 121.0, 117.0, 62.3, 49.9, 49.3, 46.0, 41.4, 14.0; GCMS (EI, 70 eV): m/z (%): 262 (66, M+),
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189 (24), 161 (65), 132 (100), 119 (32), 104 (29), 91 (18), 77 (31), 56 (51), 42 (18); HRMS (ESI-
ion trap): m/z= Calcd for [(C14H18O3N2)H]+: 263.1390, found: 263.1389.
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(3g) ethyl 2-(4-benzylpiperazin-1-yl)-2-oxoacetate
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Yellowish liquid; 245 mg, yield- 89%; IR (Neat): 1739, 1667 cm–1; 1H NMR (400 MHz, CDCl3): δ
7.35-7.25 (m, 5H), 4.35-4.29 (q, 2H), 3.64 (t, 2H), 3.54 (s, 2H), 3.43 (t, 2H), 2.50-2.46 (m, 4H),
13
1.35 (t, 3H); C NMR (75 MHz, CDCl3): δ 162.8, 160.2, 137.3, 129.1, 128.4, 127.4, 62.8, 62.1,
52.8, 52.2, 46.1, 41.4, 14.0; GCMS (EI, 70 eV): m/z (%): 276 (6, M+), 247 (2), 203 (9), 199 (4),
185 (5), 175 (19), 146 (20), 132 (11), 111 (3), 91 (100); HRMS (ESI- ion trap): m/z= Calcd for
[(C15H20O3N2)H]+: 277.1547, found: 277.1548.
(3h) ethyl 2-(4-(2-fluorophenyl)piperazine-1-yl)-2-oxoacetate
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Yellowish liquid; 243 mg, yield- 87%; IR (Neat): 1739, 1668 cm–1; (1H and C NMR spectra are
1
described for both rotamers about the amide bond) H NMR (400 MHz, CDCl3): δ 7.10-6.91 (m,
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4H), 4.35 (q, 2H), 3.81 (t, 2H), 3.61 (t, 2H), 3.15-3.11 (m, 4H), 1.38 (t, 3H); C NMR (75 MHz,
CDCl3): δ 162.6, 160.2, 157.4, 154.2, 139.3, 139.2, 124.7, 124.6, 123.6, 123.5, 119.4, 119.4, 116.5,
116.2, 62.3, 50.8, 50.8, 50.1, 50.1, 46.3, 41.5, 14.0; GCMS (EI, 70 eV): m/z (%): 280 (43, M+), 251
(3), 207 (35), 179 (46), 150 (100), 137 (41), 122 (36), 109 (18), 95 (12), 70 (16), 56 (62), 42 (22);
HRMS (ESI- ion trap): m/z= Calcd for [(C14H17O3N2F)H]+: 281.1296, found: 281.1295.
(3i) ethyl 2-(diallylamino)-2-oxoacetate1c
Yellowish liquid; 181 mg, yield- 92%; IR (Neat): 1739, 1667 cm–1; 1H NMR (400 MHz, CDCl3): δ
5.83-5.71 (m, 2H), 5.27-5.18 (m, 4H), 4.33 (q, J= 7.16Hz, 2H), 4.01-4.00 (m, 2H), 3.88-3.85 (m,
2H), 1.36 (t, J= 7.16Hz, 3H); 13C NMR (75 MHz, CDCl3): δ 162.8, 161.7, 132.3, 131.5, 119.0,
118.7, 62.1, 49.6, 46.3, 14.0; GCMS (EI, 70 eV): m/z (%): 197 (1, M+), 156 (7), 124 (35), 96 (5),
81 (10), 56 (7), 41 (100).
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(3j) ethyl 2-(dibenzylamino)-2-oxoacetate 1c
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Yellowish solid; 276 mg, yield- 93%; IR (KBr): 1732, 1661 cm–1; (1H and C NMR spectra are
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described for both rotamers about the amide bond) H NMR (400 MHz, CDCl3): δ 7.39-7.16 (m,
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10H), 4.54 (s, 2H), 4.49 (s, 2H), 4.38 (s, 2H), 4.33 (s, 2H), 4.33(q, 2H), 1.32 (t, 3H); 13C NMR (75
MHz, CDCl3): δ 165.1, 163.1, 162.4, 135.9, 135.5, 135.2, 134.9, 128.9, 128.9, 128.8, 128.6, 128.5,
128.3, 128.3, 128.0, 127.9, 127.8, 62.3, 50.3, 46.2, 46.0, 14.0; GCMS (EI, 70 eV): m/z (%): 206
(58, M+), 178 (4), 132 (17), 106 (11), 91 (100), 65 (13).
(3m) ethyl 2-(benzyl(methyl)amino)-2-oxoacetate
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Yellowish liquid; 194 mg, yield- 88%; IR (Neat): 1736, 1655 cm–1; (1H and C NMR spectra are
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described for both rotamers about the amide bond) H NMR (400 MHz, CDCl3): δ 7.37-7.26 (m,
5H), 4.60 (s, 2H), 4.45 (s, 2H), 4.39-4.31 (m, 2H), 2.90 (s, 3H), 2.87 (s, 3H), 1.38 (t, 3H), 1.33 (t,
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3H); C NMR (75 MHz, CDCl3): δ 163.1, 163.0, 162.1, 162.0, 135.5, 135.1, 128.9, 128.8, 128.3,
127.9, 127.7, 62.2, 62.1, 53.7, 49.9, 34.6, 31.6, 14.0, 14.0; GCMS (EI, 70 eV): m/z (%): 221 (2,
M+), 192 (2), 147 (16), 118 (9), 119 (10), 91 (100), 65 (12); HRMS (ESI- ion trap): m/z= Calcd for
[(C12H15O3N)Na]+: 244.0944, found: 244.0944.
(3n) ethyl 2-(3,4-dihydroisoquinoline-2(1H)-yl)-2-oxoacetate
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Yellowish liquid; 209 mg, yield- 90%; IR (Neat): 1739, 1660 cm–1; (1H and C NMR spectra are
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described for both rotamers about the amide bond) H NMR (400 MHz, CDCl3): δ 7.26-7.06 (m,
4H), 4.75 (s, 2H), 4.63 (s, 2H), 4.38 (q, J= 7.16Hz, 2H), 3.86 (t, 2H), 3.68 (t, 2H), 2.96-2.90 (m,
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2H), 1.41 (t, 3H), 1.38 (t, 3H); C NMR (75 MHz, CDCl3): δ 162.8, 162.7, 160.8, 160.4, 134.3,
133.5, 131.7, 131.6, 129.0, 128.7, 127.3, 126.9, 126.8, 126.7, 126.1, 62.2, 47.5, 43.8, 43.7, 39.6,
29.7, 29.3, 28.0, 14.1; GCMS (EI, 70 eV): m/z (%): 233 (41, M+), 204 (9), 160 (59), 159 (24), 142
(53), 131 (100), 117 (36), 115 (23), 104 (30), 91 (13), 77 (19); HRMS (ESI- ion trap): m/z= Calcd
for [(C13H15O3N)Na]+: 256.0944, found: 256.0943.
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(3o) ethyl 2-(isopropyl(methyl)amino)-2-oxoacetate
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Yellowish liquid; 162 mg, yield- 94%; IR (Neat): 1736, 1655 cm–1. (1H and C NMR spectra are
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described for both rotamers about the amide bond) H NMR (400 MHz, CDCl3): δ 4.74 (m, 1H),
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4.33 (q, J= 7.16Hz, 2H), 3.83 (m, 1H), 2.84 (s, 3H), 1.36 (t, J= 7.16Hz, 3H), 1.24 (d, J= 6.64Hz,
3H), 1.17 (d, J= 6.80Hz, 3H); 13C NMR (75 MHz, CDCl3): δ 163.5, 163.3, 161.8, 161.6, 61.9, 49.6,
44.1, 28.6, 24.9, 20.2, 18.9, 14.0; GCMS (EI, 70 eV): m/z (%): 173 (4, M+), 144 (15), 130 (9), 100
(44), 58 (60), 43 (100); HRMS (ESI- ion trap): m/z= Calcd for [(C8H15O3N)H]+: 174.1125, found:
174.1124.
(3p) methyl 2-oxo-2-(piperidine-1-yl)acetate4b
Yellowish liquid; 159 mg, yield- 93%; IR (Neat): 1742, 1660 cm–1; 1H NMR (400 MHz, CDCl3): δ
3.87 (s, 3H), 3.57 (t, J= 5.76Hz, 2H), 3.34 (t, J= 5.6Hz, 2H), 1.72-1.59 (m, 6H); 13C NMR (75
MHz, CDCl3): δ 163.6, 160.0, 52.5, 47.3, 42.3, 26.2, 25.1, 24.3; GCMS (EI, 70 eV): m/z (%): 171
(23, M+), 112 (89), 83 (14), 69 (100), 56 (20), 41 (74).
(3q) butyl 2-oxo-2-(piperidine-1-yl)acetate4b
Yellowish liquid; 200 mg, yield- 94%; IR (Neat): 1739, 1661 cm–1; 1H NMR (400 MHz, CDCl3): δ
4.27 (t, J= 6.68Hz, 2H), 3.56 (t, J= 5.76Hz, 2H), 3.33 (t, J= 5.6Hz, 2H), 1.74-1.61 (m, 8H), 1.47-
1.37 (m, 2H), 0.95 (t, J= 7.4Hz, 3H); 13C NMR (75 MHz, CDCl3): δ 163.4, 160.4, 65.7, 47.3, 42.1,
30.4, 26.2, 25.1, 24.4, 19.0, 13.6; GCMS (EI, 70 eV): m/z (%): 213 (10, M+), 156 (7), 112 (100), 83
(9), 69 (70), 56 (11), 41 (46).
Acknowledgment.
We are thankful to Dr. C.V. Rode from National Chemical Laboratory, Pune for providing HR-MS
analysis of products. The authors STG is thankful to CSIR (Council of Scientific and Industrial
Research) New Delhi, India for providing senior research fellowship
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Supporting Information Available:
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Copies of H and 13C NMR of the products. This material is available free of charge via the
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Internet at http://pubs.acs.org.
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