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Synlett 2008(11): 1673-1678  
DOI: 10.1055/s-2008-1078482
LETTER
© Georg Thieme Verlag Stuttgart · New York

Straightforward and Regiospecific Synthesis of Pyrazole-5-carboxylates from Unsymmetrical Enaminodiketones

Fernanda A. Rosa, Pablo Machado, Pâmela S. Vargas, Helio G. Bonacorso, Nilo Zanatta, Marcos A. P. Martins*
Núcleo de Química de Heterociclos (NUQUIMHE), Departamento de Química, Universidade Federal de Santa Maria, 97.105-900 Santa Maria, RS, Brazil
Fax: +55(55)32208031; e-Mail: mmartins@base.ufsm.br;
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Publication History

Received 26 January 2008
Publication Date:
11 June 2008 (online)

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Abstract

A series of 4-substituted 1H-pyrazole-5-carboxylates was prepared from the cyclocondensation reaction of unsymmetrical enaminodiketones [RC(O)C(=CNMe2)C(O)CO2Et, where R = Ph, 4-MeOC6H4, 4-ClC6H4, 4-FC6H4, 4-O2NC6H4, thien-2-yl, benzofur-2-yl, CCl3 and CF3] with tert-butylhydrazine hydrochloride or carboxymethylhydrazine. The compounds were obtained regiospecifically and in good to excellent yields (73-94%). In addition, 5-carboxyethyl-1-(1,1-dimethylethyl)-1H-pyrazole-4-carboxylic acid was synthesized from regiospecific conversion of ethyl 4-(2,2,2-trichloroacetyl)-1-(1,1-dimethylethyl)-1H-pyrazole-5-carboxylate. The carbonyl substitution reaction was regiospecific for the trichloroacetyl group and did not affect the ester group.

Key words

enones - cyclizations - regioselectivity - pyrazoles - ­heterocycles

    References and Notes

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15

4-Dimethylamino-3-(4-methoxybenzoyl)-2-oxobut-3-enoic Acid Ethyl Ester (1b): yield: 86%; oil. 1H NMR (200 MHz, CDCl3): δ = 1.11 (t, 3 H, OCMe), 2.78 (s, 3 H, NMe2), 3.33 (s, 3 H, NMe2), 3.85 (s, 3 H, OMe), 3.93 (q, 2 H, OCH2), 6.91-7.75 (m, 4 H, C6H4), 7.85 (s, 1 H, H4). 13C NMR (100 MHz, CDCl3): δ = 13.5 (OCMe), 42.2 (NMe2), 47.7 (NMe2), 55.3 (OMe), 61.3 (OCH2), 107.8 (C3), 113.5, 131.3, 132.8, 162.9 (C6H4), 158.4 (C4), 164.6 (C1), 183.1 (C2), 192.3 (C3′). MS (EI, 70 eV): m/z (%) = 305 (3) [M+], 232 (29), 135 (100), 107 (4), 77 (10). Anal. Calcd for C16H19NO5: C, 62.94; H, 6.27; N, 4.59. Found: C, 63.15; H, 6.43; N, 4.81. 3-(Benzofuran-2-carbonyl)-4-dimethylamino-2-oxobut-3-enoic Acid Ethyl Ester (1g): yield: 89%; oil. 1H NMR (200 MHz, CDCl3): δ = 1.03 (t, 3 H, OCMe), 2.91 (s, 3 H, NMe2), 3.40 (s, 3 H, NMe2), 3.94 (q, 2 H, OCH2), 7.28-7.66 (m, 5 H, benzofur-2-yl), 7.90 (s, 1 H, H4). 13C NMR (100 MHz, CDCl3): δ = 13.5 (OCMe), 42.8 (NMe2), 48.2 (NMe2), 61.7 (OCH2), 107.6 (C3), 112.1, 113.3, 122.9, 123.7, 126.9, 127.7, 154.2, 155.4 (benzofur-2-yl), 159.5 (C4), 164.0 (C1), 180.8 (C2), 182.5 (C3′). MS (EI, 70 eV): m/z (%) = 315 (10) [M+], 242 (77), 169 (39), 145 (100), 89 (33). Anal. Calcd for C17H17NO5: C, 64.75; H, 5.43; N, 4.44. Found: C, 64.92; H, 5.56; N, 4.67.

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General Procedure for the Synthesis of Pyrazoles 2: A mixture of enaminodiketone 1 (5 mmol) and tert-butyl-hydrazine hydrochloride (0.748 g, 6 mmol) was stirred under reflux in anhyd EtOH (20 mL) for 1 h. Then the mixture was cooled to r.t. and the solvent was evaporated under vacuum. The residue was washed with H2O (20 mL) and extracted with CH2Cl2 (3 × 30 mL) and the organic layers were dried over Na2SO4, and evaporated under vacuum. Recrystalli-zation from hexane afforded the pure pyrazoles 2a-i.
Ethyl 4-Benzoyl-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2a): yield: 1.15 g (77%); oil. 1H NMR (200 MHz, CDCl3): δ = 1.34 (t, 3 H, OCMe), 1.69 (s, 9 H, t-Bu), 4.37 (q, 2 H, OCH2), 7.51-7.84 (m, 5 H, Ph), 7.71 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.5 (Me), 29.6 (3 × Me), 62.6 (OCH2), 62.9 [NC(CH)3], 122.4 (C4), 128.4, 128.9, 132.4, 138.8 (Ph), 136.9 (C5), 138.3 (C3), 163.0 (CO2), 188.5 (CO). MS (EI, 70 eV): m/z (%) = 300(16) [M+], 245 (49), 199 (100), 167 (72), 139 (49), 121 (14), 105 (37), 77 (38). Anal. Calcd for C17H20N2O3: C, 67.98; H, 6.71; N, 9.33. Found: C, 67.93; H, 6.62; N, 9.15.
Ethyl 4-(4-Methoxybenzoyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2b): yield: 1.48 g (90%); oil. 1H NMR (200 MHz, CDCl3): δ = 1.33 (t, 3 H, OCMe), 1.69 (s, 9 H, t-Bu), 3.87 (s, 3 H, OMe), 4.37 (q, 2 H, OCH2), 6.96-7.86 (m, 4 H, C6H4), 7.70 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.5 (Me), 29.6 (3 × Me), 55.4 (OMe), 62.6 (OCH2), 62.8 [NC(CH)3], 113.6, 131.0, 131.3, 163.1 (C6H4), 122.9 (C4), 136.7 (C5), 138.4 (C3), 163.1 (CO2), 187.2 (CO). MS (EI, 70 eV): m/z (%) = 330 (45) [M+], 274 (32), 230 (100), 201 (26), 167 (20), 139 (29), 135 (54), 107 (8), 77 (14). Anal. Calcd for C18H22N2O4: C, 65.44; H, 6.71; N, 8.48. Found: C, 65.52; H, 6.65; N, 8.31. Ethyl 4-(4-Chlorobenzoyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2c): yield: 1.22 g (73%); mp 54-56 °C. 1H NMR (200 MHz, CDCl3): δ = 1.35 (t, 3 H, OCMe), 1.69 (s, 9 H, t-Bu), 4.39 (q, 2 H, OCH2), 7.46-7.79 (m, 4 H, C6H4), 7.67 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.6 (3 × Me), 62.8 (OCH2), 63.1 [NC(CH)3], 122.1 (C4), 128.7, 130.3, 138.3, 138.6 (C6H4), 131.7 (C5), 136.6 (C3), 162.9 (CO2), 187.2 (CO). MS (EI, 70 eV): m/z (%) = 334 (15) [M+], 279 (46), 233 (89), 199 (70), 167 (76), 139 (100), 111 (28). Anal. Calcd for C17H19ClN2O3: C, 60.99; H, 5.72; N, 8.37. Found: C, 60.83; H, 5.57; N, 8.13. Ethyl 4-(4-Fluorobenzoyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2d): yield: 1.32 g (83%); mp 53-55 °C. 1H NMR (200 MHz, CDCl3): δ = 1.35 (t, 3 H, OCMe), 1.69 (s, 9 H, t-Bu), 4.40 (q, 2 H, OCH2), 7.16-7.88 (m, 4 H, C6H4), 7.68 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.6 (3 × Me), 62.7 (OCH2), 63.0 [NC(CH)3], 115.5 (d, 2 J = 21 Hz, C6H4), 122.3 (C4), 131.5 (d, 3 J = 9 Hz, C6H4), 134.6 (d, 4 J = 3 Hz, C6H4), 136.9 (C5), 138.6 (C3), 162.9 (CO2), 165.3 (d, 1 J = 254 Hz, C6H4), 187.0 (CO). MS (EI, 70 eV): m/z (%) = 318 (12) [M+], 263 (42), 217 (100), 189 (21), 167 (50), 139 (41), 123 (60), 95 (43). Anal. Calcd for C17H19FN2O3: C, 64.14; H, 6.02; N, 8.80. Found: C, 63.94; H, 5.99; N, 8.53. Ethyl 1-(1,1-Dimethylethyl)-4-(4-nitrobenzoyl)-1 H -pyrazole-5-carboxylate (2e): yield: 1.57 g (91%); mp 84-85 °C. 1H NMR (200 MHz, CDCl3): δ = 1.39 (t, 3 H, OCMe), 1.70 (s, 9 H, t-Bu), 4.43 (q, 2 H, OCH2), 7.67 (s, 1 H, H3), 8.00-8.34 (m, 4 H, C6H4). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.6 (3 × Me), 62.9 (OCH2), 63.4 [NC(CH)3], 121.4 (C4), 123.7, 129.7, 143.3, 149.8 (C6H4), 137.3 (C5), 138.8 (C3), 162.7 (CO2), 186.5 (CO). MS (EI, 70 eV): m/z (%) = 345 (15) [M+], 290 (96), 244 (100), 198 (22), 167 (57), 150 (20), 139 (54), 104 (19). Anal. Calcd for C17H19FN3O5: C, 59.12; H, 5.55; N, 12.17. Found: C, 58.75; H, 5.18; N, 11.94.
Ethyl 1-(1,1-Dimethylethyl)-4-(thiophene-2-carbonyl)-1 H -pyrazole-5-carboxylate (2f): yield: 1.21 g (79%); oil. 1H NMR (200 MHz, CDCl3): δ = 1.36 (t, 3 H, OCMe), 1.69 (s, 9 H, t-Bu), 4.42 (q, 2 H, OCH2), 7.17-7.77 (m, 3 H, thien-2-yl), 7.91 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.6 (3 × Me), 62.7 (OCH2), 63.0 [NC(CH)3], 122.4 (C4), 127.9, 132.7, 133.3, 143.9 (thien-2-yl), 136.8 (C5), 137.6 (C3), 162.9 (CO2), 179.4 (CO). MS (EI, 70 eV): m/z (%) = 306 (28) [M+], 251 (32), 206 (100), 178 (47), 139 (36), 111 (61), 83 (6). Anal. Calcd for C15H18N2O3S: C, 58.80; H, 5.92; N, 9.14. Found: C, 58.61; H, 6.21; N, 9.26. Ethyl 4-(Benzofuran-2-carbonyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2g): yield: 1.46 g (86%); mp 84-85 °C. 1H NMR (200 MHz, CDCl3): δ = 1.40 (t, 3 H, OCMe), 1.70 (s, 9 H, t-Bu), 4.46 (q, 2 H, OCH2), 7.31-8.32 (m, 5 H, benzofur-2-yl), 7.61 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.6 (3 × Me), 62.8 (OCH2), 63.0 [NC(CH)3], 112.2, 113.6, 123.1, 123.9, 126.9, 128.0, 153.0, 155.5 (benzofur-2-yl), 121.2 (C4), 137.5 (C5), 138.6 (C3), 163.2 (CO2), 175.8 (CO). MS (EI, 70 eV): m/z (%) = 340 (100) [M+], 284 (74), 240 (78), 211 (73), 195 (49), 167 (17), 145 (44), 139 (39), 121 (17), 89 (36). Anal. Calcd for C19H20N2O4: C, 67.05; H, 5.92; N, 8.23. Found: C, 67.44; H, 6.15; N, 8.01. Ethyl 4-(2,2,2-Trichloroacetyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2h): yield: 1.33 g (78%); mp 96-98 °C. 1H NMR (200 MHz, CDCl3): δ = 1.43 (t, 3 H, OCMe), 1.66 (s, 9 H, t-Bu), 4.50 (q, 2 H, OCH2), 8.10 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.5
(3 × Me), 63.2 (OCH2), 63.5 [NC(CH)3], 95.3 (CCl3), 113.1 (C4), 139.3 (C3), 140.2 (C5), 162.6 (CO2), 175.2 (CO). MS (EI, 70 eV): m/z (%) = 297 (2) [M + 2 - OEt], 239 (5), 223 (20), 167 (100), 139 (50), 121 (11). Anal. Calcd for C12H15Cl3N2O3: C, 42.19; H, 4.43; N, 8.20. Found: C, 42.39; H, 4.58; N, 8.32. Ethyl 4-(2,2,2-Tri-fluoroacetyl)-1-(1,1-dimethylethyl)-1 H -pyrazole-5-carboxylate (2i): yield: 1.11 g (76%); oil. 1H NMR (200 MHz, CDCl3): δ = 1.42 (t, 3 H, OCMe), 1.66 (s, 9 H, t-Bu), 4.49 (q, 2 H, OCH2), 7.90 (s, 1 H, H3). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 29.5 (3 × Me), 63.4 (OCH2), 63.9 [NC(CH)3], 115.3 (C4), 116.2 (q, 1 J = 290 Hz, CF3), 138.7 (C5), 138.8 (C3), 162.2 (CO2), 174.2 (q, 2 J = 37 Hz, CO). MS (EI, 70 eV): m/z (%) = 292 (4) [M+], 277 (4), 237 (65), 231 (35), 223 (23), 209 (12), 191 (100), 167 (55), 139 (40), 121 (13), 69 (4). Anal. Calcd for C12H15F3N2O3: C, 49.32; H, 5.17; N, 9.59. Found: C, 49.09; H, 5.37; N, 9.86.

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Crystallographic data for compound 2h, reported in this paper, have been deposited with the Cambridge Crystallographic Data Centre (CCDC 669661). Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: +44(1223)336033 or e-mail: deposit@ccdc.cam.ac.uk.

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General Procedure for the Synthesis of Pyrazoles 3:
A mixture of enaminodiketone 1 (5 mmol) and carboxy-methylhydrazine (0.540 g, 6 mmol) was stirred at r.t. in anhyd EtOH (20 mL) for 1 h. Then the product was filtered, washed with EtOH and dried under vacuum affording the pure pyrazoles 3a-g.
Ethyl 4-Benzoyl-1 H -pyrazole-5-carboxylate (3a): yield: 0.91 g (75%); mp 196-198 °C. 1H NMR (200 MHz, CDCl3): δ = 0.93 (t, 3 H, OCMe), 4.10 (q, 2 H, OCH2), 7.47-7.87 (m, 5 H, Ph), 8.24 (s, 1 H, H3), 14.56 (br, 1 H, NH). 13C NMR (100 MHz, CDCl3): δ = 13.3 (Me), 61.4 (OCH2), 122.1 (C4), 128.3, 129.4, 133.0, 138.6 (Ph), 133.7 (C3), 141.6 (C5), 161.8 (CO2), 190.2 (CO). MS (EI, 70 eV): m/z (%) = 244 (18) [M+], 217 (6), 200(45), 171 (11), 167 (41), 139 (52), 121 (29), 105 (43), 77 (100). Anal. Calcd for C13H12N2O3: C, 63.93; H, 4.95; N, 11.47. Found: C, 64.11; H, 5.33; N, 11.76. Ethyl 4-(4-Methoxybenzoyl)-1 H -pyrazole-5-carboxylate (3b): yield: 1.16 g (85%); mp 156-158 °C. 1H NMR (200 MHz, CDCl3): δ = 1.00 (t, 3 H, OCMe), 3.88 (s, 3 H, OMe), 4.15 (q, 2 H, OCH2), 6.94-7.85 (m, 4 H, C6H4), 8.16 (s, 1 H, H3), 14.34 (br, 1 H, NH). 13C NMR (100 MHz, CDCl3): δ = 13.5 (Me), 55.4 (OMe), 61.3 (OCH2), 113.6, 131.4, 131.8, 163.6 (C6H4), 122.4 (C4), 133.2 (C3), 141.3 (C5), 161.8 (CO2), 188.9 (CO). MS (EI, 70 eV): m/z (%) = 274 (100) [M+], 247 (20), 230 (58), 201 (21), 167 (16), 139 (52), 135 (100), 121 (40), 107 (24), 91 (47), 77 (62). Anal. Calcd for C14H14N2O4: C, 61.31; H, 5.14; N, 10.21. Found: C, 61.10; H, 4.93; N, 9.99.
Ethyl 4-(4-Chlorobenzoyl)-1 H -pyrazole-5-carboxylate (3c): yield: 1.20 g (86%); mp 190-192 °C. 1H NMR (200 MHz, CDCl3): δ = 0.98 (t, 3 H, OCMe), 4.14 (q, 2 H, OCH2), 7.45-7.81 (m, 4 H, C6H4), 8.22 (s, 1 H, H3), 14.45 (br, 1 H, NH). 13C NMR (100 MHz, DMSO-d 6): δ = 13.6 (Me), 60.7 (OCH2), 121.1 (C4), 128.8, 130.8, 136.8, 138.0 (C6H4), 133.0 (C3), 142.7 (C5), 161.9 (CO2), 188.2 (CO). MS (NICI, CH4): m/z (%) = 278 (100) [M+]. Anal. Calcd for C13H11ClN2O3: C, 56.03; H, 3.98; N, 10.05. Found: C, 55.77; H, 3.62; N, 9.95.
Ethyl 4-(4-Fluorobenzoyl)-1 H -pyrazole-5-carboxylate (3d): yield: 1.15 g (88%); mp 189-191 °C. 1H NMR (200 MHz, CDCl3): δ = 0.98 (t, 3 H, OCMe), 4.15 (q, 2 H, OCH2), 7.15-7.90 (m, 4 H, C6H4), 8.21 (s, 1 H, H3). 13C NMR (100 MHz, DMSO-d 6): δ = 13.6 (Me), 60.7 (OCH2), 115.7 (d, 2 J = 22 Hz, C6H4), 121.3 (C4), 131.9 (d, 3 J = 9 Hz, C6H4), 132.7 (C3), 134.8 (d, 4 J = 3 Hz, C6H4), 142.7 (C5), 161.8 (CO2), 165.0 (d, 1 J = 251 Hz, C6H4), 187.9 (CO). MS (EI, 70 eV): m/z (%) = 262 (100) [M+], 218 (76), 189 (13), 167 (67), 139 (71), 123 (64), 107 (7), 95 (82). Anal. Calcd for C13H11FN2O3: C, 59.54; H, 4.23; N, 10.68. Found: C, 59.17; H, 3.86; N, 10.67.
Ethyl 4-(4-Nitrobenzoyl)-1 H -pyrazole-5-carboxylate (3e): yield: 1.36 g (94%); mp 177-179 °C. 1H NMR (200 MHz, CDCl3): δ = 1.02 (t, 3 H, OCMe), 4.15 (q, 2 H, OCH2), 8.00-8.31 (m, 4 H, C6H4), 8.18 (s, 1 H, H3), 13.72 (br, 1 H, NH). 13C NMR (50 MHz, CDCl3): δ = 13.6 (Me), 61.8 (OCH2), 121.7 (C4), 123.7, 130.2, 143.3, 150.4 (C6H4), 135.1 (C3), 141.0 (C5), 161.1 (CO2), 188.3 (CO). MS (EI, 70 eV): m/z (%) = 289 (11) [M+], 262 (13), 245 (21), 199 (21), 167 (66), 139 (100), 122 (72), 104 (30), 76 (18). Anal. Calcd for C13H11N3O5: C, 53.98; H, 3.83; N, 14.53. Found: C, 53.99; H, 3.59; N, 14.58.
Ethyl 4-(Thiophene-2-carbonyl)-1 H -pyrazole-5-carboxylate (3f): yield: 0.92 g (74%); mp 140-142 °C. 1H NMR (200 MHz, CDCl3): δ = 1.11 (t, 3 H, OCMe), 4.25 (q, 2 H, OCH2), 7.14-7.72 (m, 3 H, thien-2-yl), 8.24 (s, 1 H, H3), 14.31 (br, 1 H, NH). 13C NMR (100 MHz, CDCl3): δ = 13.5 (Me), 61.5 (OCH2), 122.0 (C4), 128.0, 134.3, 134.4, 145.2 (thien-2-yl), 133.0 (C3), 141.3 (C5), 161.7 (CO2), 181.7 (CO). MS (NICI, CH4): m/z (%) = 250 (100) [M+]. Anal. Calcd for C11H10N2O3S: C, 52.79; H, 4.03; N, 11.19. Found: C, 52.59; H, 3.77; N, 11.28. Ethyl 4-(Benzofuran-2-carbonyl)-1 H -pyrazole-5-carboxylate (3g): yield: 1.26 g (89%); mp 158-160 °C. 1H NMR (200 MHz, CDCl3): δ = 1.08 (t, 3 H, OCMe), 4.23 (q, 2 H, OCH2), 7.32-7.71 (m, 5 H, benzofur-2-yl), 8.35 (s, 1 H, H3), 13.55 (br, 1 H, NH). 13C NMR (100 MHz, DMSO-d 6): δ = 13.6 (Me), 60.7 (OCH2), 112.1, 114.6, 120.2 (C4), 123.6, 124.0, 126.8, 128.4, 133.1 (C3), 143.3 (C5), 152.5, 155.0 (benzofur-2-yl), 162.1 (CO2), 177.0 (CO). MS (EI, 70 eV): m/z (%) = 284 (100) [M+], 257 (4), 240 (27), 211 (33), 184 (16), 167 (12), 145 (38), 139 (53), 89 (68). Anal. Calcd for C15H12N2O4: C, 63.38; H, 4.25; N, 9.85. Found: C, 63.30; H, 4.21; N, 9.97.

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Crystallographic data for compound 3d, reported in this paper, have been deposited with the Cambridge Crystallographic Data Centre (CCDC 669660). Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: +44(1223)336033 or e-mail: deposit@ccdc.cam.ac.uk.

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Procedure for the Synthesis of Pyrazole 4: To a stirred solution of 2h (0.341 g, 1 mmol) in EtOH (4 mL) was added sat. aq solution of KOH (2 mL) and stirring was continued at r.t. for 4 h. The basic solution was acidified with 2 N HCl (20 mL) in an ice-bath. Most of the solvent was removed under reduced pressure and the resulting mixture was diluted with CH2Cl2 (20 mL), and dried over Na2SO4. Evaporation of the solvent gave pyrazole 4 with a high degree of purity.
5-Carboxyethyl-1-(1,1-dimethylethyl)-1 H -pyrazole-4-carboxylic Acid (4): yield: 0.18 g (76%); mp 99-101 °C. 1H NMR (200 MHz, CDCl3): δ = 1.36 (t, 3 H, OCMe), 1.64 (s, 9 H, t-Bu), 4.44 (q, 2 H, OCH2), 7.89 (s, 1 H, H3). 13C NMR (100 MHz, CDCl3): δ = 13.6 (Me), 29.5 (3 × Me), 62.8 (OCH2), 62.9 [NC(CH)3], 113.3 (C4), 137.3 (C5), 139.3 (C3), 162.9 (CO2), 167.5 (COOH). MS (EI, 70 eV):
m z (%) = 240 (4) [M+], 225 (4), 207 (19), 195 (6), 185 (30), 167 (90), 139 (100), 121 (9), 68 (12). Anal. Calcd for C11H16N2O4: C, 54.99; H, 6.71; N, 11.66. Found: C, 55.01; H, 6.88; N, 11.72.