A novel approach for the synthesis of β-keto esters: One-pot reaction of carboxylic acids with chlorosulfonyl isocyanate

Article abstract of DOI:10.24820/ARK.5550190.P011.209

β-Keto esters were synthesized by direct carboxylation of various 4- and 5-oxo-carboxylic acid derivatives in the presence of chlorosulfonyl isocyanate in excellent yield under mild conditions. Additionally, optimization conditions were examined for synthesis β-keto esters. Finally, it has been found that trifluoroacetic acid is efficient in DCM under optimized conditions. This efficient one-pot novel method is very usefull, fair price and easy to handle of β-keto esters.

Full text of DOI:10.24820/ARK.5550190.P011.209

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A novel approach for the synthesis of β-keto esters: one-pot reaction of
carboxylic acids with chlorosulfonyl isocyanate
Ufuk Atmacaa,b
a Oltu Vocational School, Ataturk University, 25400, Oltu-Erzurum, Turkey
b Department of Chemistry, Faculty of Sciences, Atatürk University, 25240, Erzurum, Turkey
Email: uatmaca@atauni.edu.tr
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Abstract
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Published on line mm-dd-yyyy
β-Keto esters were synthesized by direct carboxylation of various 4- and 5-oxo-carboxylic acid derivatives in
the presence of chlorosulfonyl isocyanate in excellent yield under mild conditions. Additionally, optimization
conditions were examined for synthesis β-keto esters. Finally, it has been found that trifluoroacetic acid is
efficient in DCM under optimized conditions. This efficient one-pot novel method is very usefull, fair price and
easy to handle of β-keto esters.
Keywords: β-Keto ester, chlorosulfonyl isocyanate, carboxylic acid, trifluoroacetic acid, one-pot
DOI: https://doi.org/10.24820/ark.5550190.p011.209
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Introduction
β-Keto esters are multi-coupling reagents that have both a nucleophilic carbon and an electrophilic carbonyl
group. These molecules are very significant intermediates for the synthesis of a wide range of bioactive and
natural products such as 1,4-dihydropyridines, arylcoumarins, and 3,4-dihydropyrimidinones,1 chokol,2
syncarpic acid,3 and polyoxamic acid.4 Furthermore, they are also used preparation of catalysis,5 polymer
stabilization,6 synthesis of metal microfilms impregnation and liquid crystal preparation technology.7
Therefore, various methods have been investigated for the synthesis of their derivatives.1 Common methods
for the synthesis of β-keto esters mostly rely on Claisen reaction8 and related condensations of enolates with
alkyl carbonates and oxalates followed by decarbonylation.9,10
Scheme 1. Methods for the synthesis of β-keto ester derivatives
In recent years, with the increasing demands to β-keto esters, synthesis of these molecules has been
reported alkoxycarboxylation of halomethylketones with Pd-catalyzed (Scheme 1a).11 Meanwhile, synthesis of
β-keto esters by C-H insertion reactions of diazoesters with Niobium(V) chloride catalyzed were reported by
the Yadav group (Scheme 1b).12 Synthesis of β-keto esters by aza-Knoevenagel reactions of tertiary amides
have been also developed (Scheme 1c).13 Recent developments in the synthetic use of CSI are known in the
literature.14 Previously, we completed reaction of a range of benzoic acid derivatives with CSI that were
yielded sulfamate derivatives.15
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In this work, we reported novel and efficient one-pot synthetic method for the synthesis of β-keto esters (2a-
n) from carboxylic acid derivatives (1a-n) under mild conditions in good yields (Scheme 1).
Results and Discussion
Initially, the reaction of 5-oxo-5-phenylpentanoic acid with CSI (1a) was chosen that as the model reaction
which was carried out in various solvents, acids, bases. The solvent effect was investigated with
dichloromethane (DCM) and acetonitrile in the absence of acid and base at room temperature. In these
reactions, 2-benzoylpentanedioate (2a) was observed in 54% and 42% isolated yield, respectively. The
1
structure of dimethyl 2-benzoylpentanedioate (2a) was verified with H- and 13C-NMR, IR, and HRMS. Then,
acid or base effect was examined with the triflic acid (TfOH), trifluoroacetic acid (TFA), triethylamine (NEt3),
and pyridine. The use of TfOH gave the dimethyl 2-benzoylpentanedioate (2a) in good yield (entry 2 and 7).
The desired product 2a yielded the use of NEt3, or pyridine in poor yield (entry 4, 5, 9, and 10). The desired
product dimethyl 2-benzoylpentanedioate (2a) was obtained in 92% yield, when the reaction was performed
in DCM with TFA (entry 8).
Table 1. Model reaction for novel synthesis of dimethyl 2-benzoylpentanedioate (2a)
entry Solvents
Acid or Basea
-
Yieldb (%)
42
1
2
TfOH
TFA
53
Acetonitrile
3
4
62
NEt3
28
5
Pyridine
-
17
6
54
7
TfOH
TFA
69
CH2Cl2
8
92
9
NEt3
29
10
Pyridine
a 1 equivalent, bIsolated yield
23
Thus, the optimized reaction condition for alternative and novel intramolecular synthesis of β-keto
esters from 4- and 5-oxocarboxylic acid derivatives was concluded finally to be the use DCM as solvent with
TFA as additive under mild conditions at room temperature for 3 h.
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Table 2. Novel synthesis of β-keto esters from carboxylic acids using TFAa,b,c
aReaction conditions: 1.0 mmol of Carboxylic acid (1a-n), 1.0 mmol TFA, 1.1 mmol of CSI, 10 mL DCM, reaction
was stirred for 2h and added 2 mL MeOH for 1h, bIsolated yield, cLit.
With the above optimal reaction conditions in hand, we examined the scope of 4- and 5-oxo carboxylic
acid derivatives (1a-n) as the reaction partners. As shown in Table 2, the reactions of 4- and 5-oxo carboxylic
acid derivatives bearing electron donating groups (4−methyl, 2,5−dimethyl, 3,4−dimethyl, 2,4−dimethyl and, 4-
phenyl) with CSI proceeded smoothly to furnish 2a16 (92%), 2b (91%), 2c (89%), 2d (90%), 2e (88%), 2g[16]
(93%), 2h17 (90%), 2i (87%), 2j (86%), 2k (86%), and 2n (90%), respectively. The halogen substituted 4- and 5-
oxo-carboxylic acid derivatives (4−Br, 4−I) were observed also good reactivities, and the novel β-keto ester
derivative 2f was obtained in 87% yield. 2l18 and 2m were isolated in 87% and 84% yield, respectively, when 4-
(4-bromophenyl)-4-oxobutanoic acid (1l) and 4-(4-iodophenyl)-4-oxobutanoic acid (1m) were subjected to the
reaction with CSI.
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Scheme 2. Possible mechanism for synthesis of β-keto ester
In the first step, OH group of carboxylic acid attacks to carbonyl group of isocyanate as nucleophilic.
Intermadiate carbamate is being tautomerization (I) and following the intramolecular attack of α-carbon to
carbonyl carbamate (II, III and IV). Then, sulfamoyl chloride (NH2SO2Cl) leave from relating molecule to form
cyclic anhydride (V). Finally, β-keto ester was occured by ring opening reaction of cyclic anhydride (3).
Conclusions
A pratical novel alternative method, one-pot synthesis β-keto esters with chlorosulfonyl isocyanate from 4-
and 5-oxocarboxylic acid derivatives, were developed in high yields under mild conditions. This novel method
highly useful environmentally and benign for organic chemists and pharmaceutical industry without any metal
or oxidations, and easy to handle, under mild conditions, short reaction time. Moreover, a wide variety of β-
keto esters can be obtained in good yields.
Experimental Section
General. Solvents are commercially available and used without further purification. 4- and 5-oxo-carboxylic
acid derivatives were synthesized as in the literature.19 1H and 13C NMR spectra were recorded a Bruker 400
MHz in CDCl3 with and NMR shifts are presented as  in ppm. FTIR spectras were mesaured with a Perkin
Elmer spectrophotometers in CH2Cl2 and by solutions in 0.1mm cells. High resolution mass spectra (HRMS)
were obtained with a AB-Sciex 4600 QTOF MS spectrometer.
General procedure Synthesis of β-Keto ester. Carboxylic acid (1a-n) (1.0 eq) was dissolved in 10 mL DCM. The
reaction mixture was added CSI (1.1 eq) and TFA (1.0 eq) and stirred for 2 h at room temperature. Then, it was
added 2 mL MeOH and stirred for 1h. The reaction mixture was extracted with dichloromethane. The organic
extract was dried over sodium sulfate, filtrate and evaporation in vacuo. The resulting residue was purified by
thin-layer chromatography (TLC) on silica gel.
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Dimethyl 2-benzoylpentanedioate (2a). Yellowish oil (316 mg, yield 92%), H-NMR (CDCl3, ppm, 400 MHz): δ
2.30-2.35 (m, 2H), 2.46-2.50 (m, 2H), 3.69 (s, 3H), 3.71 (s, 3H), 4.55 (t, J 7.2 Hz, 1H), 7.50-7.53 (m, 2H), 7.60-
7.64 (m, 1H), 8.04-8.06 (m, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 24.0, 31.2, 51.7, 52.5, 52.6, 128.7, 128.8,
133.7, 135.9, 170.0, 173.2, 194.9; IR (CH2Cl2, cm-1): 3003, 2955, 2849, 1737, 1689, 1596, 1436, 1333, 1272,
1161; HRMS (ESI) calcd. for C14H15O5 [M − H]− 263.0925; found: 263.0916.
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Dimethyl 2-(4-methylbenzoyl)pentanedioate (2b). Yellowish oil (305 mg, yield 91%), H-NMR (CDCl3, ppm,
400 MHz): δ 2.28-2.32 (m, 2H), 2.42-2.47 (m, 5H), 3.67 (s, 3H), 3.68 (s, 3H), 4.50 (t, J 7.2 Hz, 1H), 7.28 (d, J 8.0,
2H), 7.92 (d, J 8.0 Hz, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 21.7, 24.0, 51.7, 52.4, 52.5, 128.9, 129.5, 133.4,
144.7, 170.1, 173.2, 194.4; IR (CH2Cl2, cm-1): 3010, 2942, 2855, 1748, 1690, 1592, 1440, 1328, 128, 1153;
HRMS (ESI−) calcd. for C14H15O5 [M − H]− 263,0925; found: 263,0916; HRMS (ESI) calcd. for C15H17O5 [M − H]−
277.1081; found: 277.1088.
Dimethyl 2-(2,5-dimethylbenzoyl)pentanedioate (2c). Yellowish oil (294 mg, yield 89%), 1H-NMR (CDCl3, ppm,
400 MHz): δ 2.25-2.28 (m, 2H), 2.35-2.44 (m, 8H), 3.67 (s, 6H), 4.40 (t, J 7.1 Hz, 1H), 7.12-7.15 (m, 1H), 7.19-
7.21 (m, 1H), 7.49-7.51 (m, 1H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 20.6, 23.9, 31.3, 33.1, 51.7, 52.4, 54.9,
129.2, 132.0, 132.6, 135.3, 135.9, 136.7, 170.1, 173.1, 198.4; IR (CH2Cl2, cm-1): 2953, 1739, 1652, 1437, 1302,
1203, 1118; HRMS (ESI) calcd. for C16H19O5 [M − H]− 291.1238; found: 291.1240.
Dimethyl 2-(3,4-dimethylbenzoyl)pentanedioate (2d). Yellowish oil (297 mg, yield 90%), 1H-NMR (CDCl3, ppm,
400 MHz): δ 2.26-2.34 (m, 8H), 2.42-2.46 (m, 2H), 3.67 (s, 3H), 3.68 (s, 3H), 4.50 (t, J 7.2 Hz, 1H), 7.23 (d, J 7.8
Hz, 1H), 7.75 (d, J 7.8 Hz, 1H), 7.79 (s, 1H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 19.8, 20.1, 24.1, 31.3, 51.7, 52.3,
52.5, 126.5, 129.8, 130.0, 133.8, 137.3, 143.5, 170.2, 173.2, 194.7; IR (CH2Cl2, cm-1): 2956, 1740, 1686, 1611,
1439, 1286, 1169; HRMS (ESI) calcd. for C16H19O5 [M − H]− 291.1238; found: 291.1224.
Dimethyl 2-(2,4-dimethylbenzoyl)pentanedioate (2e). Yellowish oil (292 mg, yield 88%), 1H-NMR (CDCl3, ppm,
400 MHz): δ 2.25-2.29 (m, 2H), 2.33-2.48 (m, 8H), 3.66 (s, 3H), 3.68 (s, 3H), 4.41 (t, J 7.2 Hz, 1H), 7.08 (s, 1H),
7.10 (s, 1H), 7.66 (d, J 7.8 Hz, 1H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 21.4, 24.0, 51.7, 52.4, 54.6, 126.5, 129.3,
133.1, 133.7, 139.7, 142.7, 170.2, 142.7, 170.3, 173.2, 197.5; IR (CH2Cl2, cm-1): 2953, 1742, 1663, 1442, 1328,
1243, 1136; HRMS (ESI) calcd. for C16H19O5 [M − H]− 291.1238; found: 291.1215.
Dimethyl 2-(4-bromobenzoyl)pentanedioate (2f). Yellowish oil (275 mg, yield 87%), 1H-NMR (CDCl3, ppm, 400
MHz): δ 2.26-2.30 (m, 2H), 2.43-2.47 (m, 2H), 3.67 (s, 3H), 3.69 (s, 3H), 4.49 (t, J 7.2 Hz, 1H), 7.63 (d, J 8.5 Hz,
2H), 7.90 (d, J 8.5 Hz, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 23.4, 31.1, 33.0, 51.7, 52.4, 129.1, 130.2, 132.2,
134.6, 169.8, 173.2, 193.9; IR (CH2Cl2, cm-1): 2952, 1735, 1686, 1583, 1435, 1329, 1272, 1171; HRMS (ESI)
calcd. for C14H14BrO5 [M − H]− 341.0030; found: 341.0035.
1
Dimethyl 2-benzoylsuccinate (2g). Yellowish oil (327 mg, yield 93%), H-NMR (CDCl3, ppm, 400 MHz): δ 3.03-
3.14 (m, 2H), 3.67 (s, 3H), 3.68 (s, 3H), 4.89 (t, J 7.2 Hz, 1H), 7.48 (d, J 7.8 Hz, 2H), 7.58-7.61 (m, 1H), 8.04 (d, J
7.3 Hz, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 33.1, 49.3, 52.1, 52.9, 128.8, 128.9, 133.8, 135.8, 169.2, 171.7,
194.0; IR (CH2Cl2, cm-1): 3003, 2955, 2849, 1737, 1689, 1596, 1436, 1333, 1272, 1161; HRMS (ESI) calcd. for
C13H14O5 [M − H]− 250.0847; found: 250.0832.
1
Dimethyl 2-(4-methylbenzoyl)succinate (2h). Yellowish oil (309 mg, yield 90%), H-NMR (CDCl3, ppm, 400
MHz): δ 2.42 (s, 3H), 3.05-3.08 (m, 2H), 3.67 (s, 3H), 3.69 (s, 3H), 4.87 (t, J 7.2 Hz, 1H), 7.29 (d, J 8.2 Hz, 2H),
7.93 (d, J 8.2 Hz, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 28.9, 33.1, 49.2, 52.1, 52.8, 129.1, 129.5, 133.3,
144.8, 169.3, 171.8, 193.5; IR (CH2Cl2, cm-1): 2953, 2826, 1737, 682, 1607, 1436, 1255, 1165; HRMS (ESI) calcd.
for C14H15O5 [M − H]− 263.0925; found: 263.0904.
1
Dimethyl 2-(2,5-dimethylbenzoyl)succinate (2i). Yellowish oil (293 mg, yield 87%), H-NMR (CDCl3, ppm, 400
MHz): δ 2.37 (s, 3H), 2.41 (s, 3H), 3.01-3.11 (m, 2H), 3.67 (s, 3H), 3.69 (s, 3H), 4.76 (t, J 7.2 Hz, 1H), 7.23-7.25
(m, 1H), 7.76-7.80 (m, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 20.4, 21.0, 32.9, 51.9, 52.1, 52.7, 129.3, 131.9,
132.6, 135.3, 135.9, 136.7, 169.3, 171.8, 197.5; IR (CH2Cl2, cm-1): 2951, 1734, 1680, 1432, 1272, 1170; HRMS
(ESI) calcd. for C15H17O5 [M − H]− 277.1081; found: 277.1090.
1
Dimethyl 2-(3,4-dimethylbenzoyl)succinate (2j). Yellowish oil (290 mg, yield 86%), H-NMR (CDCl3, ppm, 400
MHz): δ 2.32 (s, 6H), 2.98-3.11 (m, 2H), 3.67 (s, 3H), 3.69 (s, 3H), 4.87 (t, J 7.2 Hz, 1H), 7.11-7.22 (m, 2H), 7.58
(s, 1H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 19.8, 20.1, 33.1, 49.1, 52.1, 52.8, 126.7, 129.9, 130.0, 133.6, 137.2,
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143.6, 169.4, 171.8, 193.8; IR (CH2Cl2, cm-1): 2954, 1738, 1684, 1605, 1438, 1276, 1174; HRMS (ESI) calcd. for
C15H17O5 [M − H]− 277.1081; found: 277.1054.
Dimethyl 2-(2,4-dimethylbenzoyl)succinate (2k). Yellowish oil (291 mg, yield 86%), H-NMR (CDCl3, ppm, 400
1
MHz): δ 2.35 (s, 3H), 2.46 (s, 3H), 2.94-3.11 (m, 2H), 3.67 (s, 3H), 3.68 (s, 3H), 4.77 (t, J 6.6 Hz, 1H), 7.08-7.11
(m, 2H), 7.74 (d, J 7.8, Hz, 1H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 21.3, 21.4, 33.1, 51.6, 52.1, 52.7, 126.4,
129.4, 133.0, 133.7, 139.6, 142.7, 169.5, 171.8, 196.6; IR (CH2Cl2, cm-1): 2955, 2893, 1741, 1683, 1439, 1203,
1173; HRMS (ESI) calcd. for C15H17O5 [M − H]− 277.1081; found: 277.1074.
1
Dimethyl 2-(4-bromobenzoyl)succinate (2l). Yellowish oil (279 mg, yield 87%), H-NMR (CDCl3, ppm, 400
MHz): δ 3.01-3.17 (m, 2H), 3.67 (s, 3H), 3.68 (s, 3H), 4.82 (dd, J 6.2, 8.1 Hz, 1H), 7.63-7.65 (m, 2H), 7.89-7.92
(m, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 33.0, 49.1, 52.2, 53.0, 129.1, 130.4, 132.1, 134.6, 168.8, 171.7,
193.1; IR (CH2Cl2, cm-1): 2954, 1737, 1688, 1585, 1437, 1331, 1274, 1173; HRMS (ESI) calcd. for C13H12BrO5 [M −
H]− 326.9874; found: 326.9863.
Dimethyl 2-(4-iodobenzoyl)succinate (2m). Yellowish oil (260 mg, yield 84%), 1H-NMR (CDCl3, ppm, 400 MHz):
δ 2.99-3.16 (m, 2H), 3.67 (s, 3H), 3.68 (s, 3H), 4.81 (dd, J 6.2 , 8.2 Hz, 1H), 7.73-7.76 (m, 2H), 7.85-7.88 (m, 2H);
13C-NMR (CDCl3, ppm, 100 MHz): δ 33.0, 49.1, 52.2, 53.0, 102.1, 130.2, 135.2, 138.1, 168.8, 171.7, 193.5; IR
(CH2Cl2, cm-1): 2952, 2833, 1737, 1687, 1581, 1437, 1272, 1071; HRMS (ESI) calcd. for C13H12IO5 [M − H]−
374.9735; found: 374.9732.
Dimethyl 2-([1,1'-biphenyl]-4-carbonyl)succinate (2n). Yellow solid (289 mg, yield 90%), 1H-NMR (CDCl3, ppm,
400 MHz): δ 3.03-3.18 (m, 2H), 3.68 (s, 3H), 3.70 (s, 3H), 4.93 (t, J 7.2 Hz, 1H), 7.41-7.50 (m, 3H), 7.62-7.73 (m,
4H), 8.11-8.14 (m, 2H); 13C-NMR (CDCl3, ppm, 100 MHz): δ 33.1, 49.2, 52.2, 52.9, 127.3, 127.4, 128.4, 129.0,
129.6, 134.5, 139.7, 146.5, 169.2, 171.8, 193.6; IR (CH2Cl2, cm-1): 2953, 1736, 682, 603, 1436, 1274, 1172;
HRMS (ESI) calcd. for C19H17O5 [M − H]− 325.1081; found: 325.1071.
1
3-Benzoyldihydro-2H-pyran-2,6(3H)-dione (3). Reaction mixture H-NMR (CDCl3, ppm, 400 MHz): δ 2.31-2.47
(m, 2H), 2.93-2.96 (m, 2H), 4.92 (t, J 5.3 Hz, 1H), 7.53-7.59 (m, 2H), 7.67-7.73 (m, 1H), 7.96-7.98 (m, 2H).
Acknowledgements
We gratefully acknowledge Atatürk University, Faculty of Sciences, Department of Chemistry, for support of
this work
Supplementary Material
Experimental details, 1H- and 13C-NMR spectra for the products are provided in Supporting Information File.
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