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Synlett 2014; 25(2): 217-220
DOI: 10.1055/s-0033-1340055
letter
© Georg Thieme Verlag Stuttgart · New York

Simple Synthesis of 2-Aminoaryliminophosphoranes from N-Aryl-2-nitroso­anilines and Their Application in 2-Aminobenzimidazole Synthesis

Emilia Łukasik
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw,, Poland   Fax: +48(22)6326681   Email: zbigniew.wrobel@icho.edu.pl
,
Zbigniew Wróbel*
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warsaw,, Poland   Fax: +48(22)6326681   Email: zbigniew.wrobel@icho.edu.pl
› Author Affiliations
Further Information

Publication History

Received: 13 September 2013

Accepted after revision: 01 October 2013

Publication Date:
12 November 2013 (online)

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Abstract

Condensation of N-aryl-2-nitrosoanilines with triphenylphosphine leads efficiently to substituted aryliminophos­phoranes which, in turn, react with alkyl isocyanates furnishing 2-alkylaminobenzimidazole derivatives in high yields.

Key words

cyclization - condensation - heterocycles - annulation
 

  • References and Notes

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      • Reactions of the nitroso group with trivalent phosphorous compounds found in the literature are more complex, rarely leading to iminophosphorane-type products:
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  • 10 General Procedure for the Synthesis of 3 To a stirred suspension of Ph3P (3275 mg, 12.5 mmol) in dry MeCN (25 mL) solid N-aryl-2-nitrosoaniline 1 (5 mmol) was added portionwise over 30 min under external cooling with cold water, and the mixture was stirred at r.t. overnight. The precipitated solid was filtered off, and the filtrate was concentrated under vacuum and chromatographed using hexane–EtOAc gradient elution (8:1 to 2:1). An analytically pure sample of the product was obtained by recrystallization from EtOAc–hexane.
  • 11 Analytical Data for Novel Products 3 Compound 3a: pale yellow crystals; mp 164–167 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.26 (s, 3 H), 6.22 (d, J = 8.2 Hz, 1 H), 6.32 (dd, J = 8.2, 2.5 Hz, 1 H), 6.95 (t, J = 2.6 Hz, 1 H), 7.12 (s, 4 H), 7.55–7.61 (m, 7 H), 7.62–7.66 (m, 3 H), 7.73–7.78 (m, 6 H). 13C NMR (125 MHz, DMSO-d 6): δ = 20.3, 110.8, 117.5, 118.8, 119.2 (d, J CP = 10 Hz), 120.8, 129.0 (d, J CP = 12 Hz), 129.5 (d, J CP = 99 Hz), 129.6, 129.7, 132.1 (d, J CP = 10 Hz), 132.2 (d, J CP = 2 Hz), 137.5, 139.1 (d, J CP = 20 Hz), 140.0. Ms (EI): m/z (%) = 495 (19), 494 950), 493 (50), 492 (100), 262 (44), 183 (45). HRMS (EI): m/z calcd for C31H26N2 31P35Cl: 492.1522; found: 492.1529. Compound 3b: pale yellow crystals; mp 188–190 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.24 (s, 3 H), 3.55 (s, 3 H), 5.92–5.98 (m, 1 H), 6.18–6.25 (m, 1 H), 6.65–6.71 (m, 1 H), 7.08 (s, 4 H), 7.52–7.65 (m, 10 H), 7.71–7.80 (m, 6 H). 13C NMR (125 MHz, DMSO-d 6): δ = 20.3, 54.9, 99.9, 102.3, 117.7, 118.5 (d, J CP = 9 Hz), 128.7, 128.9 (d, J CP = 12 Hz), 129.6, 130.4 (d, J CP = 99 Hz), 132.0, 132.1, 137.9 (d, J CP = 20 Hz), 140.7, 151.5 (one C missing). MS (EI): m/z (%) = 490 (11), 489 (46), 488 (100), 262 (32), 183 (34). HRMS (EI): calcd for C32H29N2 31PO35Cl: 488.2018; found: 488.2014. Compound 3c: grey crystals; mp 183–185 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.17 (s, 6 H), 5.74 (s, 1 H), 6.18 (s, 2 H), 7.06–7.12 (m, 2 H), 7.15–7.18 (m, 2 H), 7.56–7.67 (m, 9 H), 7.77–7.83 (m, 6 H). 13C NMR (125 MHz, DMSO-d 6): δ = 17.9, 108.1, 115.7, 118.7 (d, J CP = 10 Hz), 121.2, 125.6, 128.2, 129.0 (d, J CP = 12 Hz), 129.9 (d, J CP = 99 Hz), 132.1 (d, J CP = 9 Hz), 132.2 (d, J CP = 3 Hz), 135.4, 136.3, 139.6, 142.1 (d, J CP = 20 Hz). MS (EI): m/z (%) = 509 (17), 508 (51), 507 (51), 506 (100), 262 (55), 183 (62). HRMS (EI): m/z calcd for C32H28N2 31P35Cl: 506.1679; found: 506.1678. Compound 3d: dark green solid; mp 131–133 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 6.18–6.26 (m, 2 H), 6.89 (dt, J = 10.8, 2.7 Hz, 1 H), 7.18–7.22 (m, 2 H), 7.27–7.30 (m, 2 H), 7.54–7.59 (m, 6 H), 7.61–7.66 (m, 3 H), 7.71–7.77 (m, 6 H), 7.85 (s, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 101.1 (d, J CF = 26 Hz), 104.9 (d, J CF = 21 Hz), 118.6, 118.7 (d, J CP = 19 Hz), 123.0, 129.0 (d, J CP = 12 Hz), 130.5 (d, J CP = 99 Hz), 132.1 (d, J CP = 10 Hz), 135.9 (d, J CP = 2 Hz), 136.9 (d, J CF = 10 Hz), 137.0 (d, J CF = 11 Hz), 142.0, 154.6 (d, J CF = 232). MS (EI): m/z (%) = 499 (13), 498 (44), 497 (43), 496 (100), 262 (58), 183 (55). HRMS (EI): m/z calcd for C30H23N2 31P35ClF: 496.1271; found: 496.1270. Compound 3e: grey crystals; mp 191–193 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.26 (s, 3 H), 6.18 (d, J = 8.2 Hz, 1 H), 6.43 (dd, J = 8.2, 2.5 Hz, 1 H), 7.06 (br s, 1 H), 7.09–7.15 (m, 4 H), 7.54–7.61 (m, 7 H), 7.63–7.66 (m, 3 H), 7.72–7.79 (m, 6 H). 13C NMR (125 MHz, DMSO-d 6): δ = 20.3, 108.4, 135.5, 118.8, 119.8 (d, J CP = 10 Hz), 120.4, 129.0 (d, J CP = 11 Hz), 129.5 (d, J CP = 96 Hz), 129.7, 129.8, 132.1 (d, J CP = 8 Hz), 132.2 (d, J CP = 2 Hz), 138.0, 139.5 (d, J CP = 21 Hz), 140.0. MS (EI): m/z (%) = 539 (39), 538 (100), 537 (49), 536 (98), 262 (61), 183 (58). HRMS (EI): m/z calcd for C31H26N2 31P79Br: 536.1017; found: 536.1016. Compound 3f: pale green crystals; mp 172–173 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.24 (s, 3 H), 6.24 (d, J = 8.3 Hz, 1 H), 6.34 (dd, J = 8.3, 2.4 Hz, 1 H), 6.88–6.92 (m, 2 H), 7.18–7.26 (m, 2 H), 7.34–7.37 (m, 1 H), 7.54 (s, 1 H), 7.56–7.61 (m, 6 H), 7.64–7.68 (m, 3 H), 7.73–7.80 (m, 6 H). 13C NMR (125 MHz, DMSO-d 6): δ = 17.6, 110.6, 117.4, 117.6, 119.1 (d, J CP = 10 Hz), 120.9, 121.2, 126.7, 127.6, 129.0 (d, J CP = 13 Hz), 129.9 (d, J CP = 99 Hz), 130.0, 132.0 (d, J CP = 10 Hz), 132.3 (d, J CP = 3 Hz), 137.5, 138.9 (d, J CP = 20 Hz), 140.6. MS (EI): m/z (%) = 494 (46), 493 (46), 492 (100), 262 (51), 183 (58). HRMS (EI): m/z calcd for C31H26N2 31P35Cl: 492.1522; found: 492.1513. Compound 3g: pale yellow crystals; mp 150–151 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 6.26 (dd, J = 8.3, 1.0 Hz, 1 H), 6.43 (dd, J = 8.3, 2.5 Hz, 1 H), 7.04 (t, J = 2.7 Hz, 1 H), 7.16–7.19 (m, 2 H), 7.27–7.30 (m, 2 H), 7.54–7.59 (m, 6 H), 7.61–7.66 (m, 3 H), 7.71–7.76 (m, 6 H), 7.81 (s, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 113.8, 118.7, 119.3, 119.9 (d, J CP = 10 Hz), 120.5, 123.0, 128.9, 129.0 (d, J CP = 12 Hz), 129.5 (d, J CP = 99 Hz), 132.1 (d, J CP = 10 Hz), 132.2 (d, J CP = 3 Hz), 137.5 (d, J CP = 20 Hz), 139.1, 142.2. MS (EI): m/z (%) = 516 (20), 515 (32), 514 (74), 513 (51), 512 (100), 262 (63), 183 (64). HRMS (EI): m/z calcd for C30H23N2 31P35Cl2: 512.0976; found: 512.0974. Compound 3h: yellow crystals; mp 185–186 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 2.25 (s, 3 H), 6.38 (d, J = 8.1 Hz, 1 H), 6,65 (dd, J = 8.1, 2.1 Hz, 1 H), 7.09–7.11 (m, 2 H), 7.19–7.20 (m, 3 H), 7.31–7.37 (m, 3 H), 7.44–7.46 (m, 2 H), 7.55–7.61 (m, 7 H), 7.64–7.67 (m, 3 H), 7.76–7.84 (m, 6 H). 13C NMR (125 MHz, CDCl3): δ = 20.7, 117.4, 118.7, 125.8, 126.2 126.4, 127.1, 128.4, 128.5 (d, J CP = 12 Hz), 128.8 (d, J CP = 11 Hz), 129.1 (d, J CP = 99 Hz), 129.7, 130.3, 131.8 (d, J CP = 3 Hz), 132.1 (d, J CP = 10 Hz), 132.5–133.0 (br signal), 141.4; some carbons not observed. MS (EI): m/z (%) = 535 (52), 534 (100), 262 (33), 183 (30). HRMS (EI): m/z calcd for C37H31N2 31P: 534.2225; found: 524.2215.
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  • 15 General Procedure for the Synthesis of 7 The requisite 3 (1 mmol) was dissolved in dry CH2Cl2 (10 mL), and isocyanate 6 (1.1 mmol) was added in one portion. The reaction flask was stoppered and stirred overnight. After completion (TLC control) the solvent was evaporated, and the residue was subjected to column chromatography (SiO2, hexane–EtOAc, 1:1). Analytically pure samples of solid products were obtained by recrystallization from hexane–EtOAc.
  • 16 Analytical Data for Novel Products 7 Compound 7aa: brown oil 1H NMR (500 MHz, DMSO-d 6): δ = 0.87 (t, J = 7.4 Hz, 3 H), 1.26–1.35 (m, 2 H), 1.52–1.59 (m, 2 H), 2.42 (s, 3 H), 3.29–3.34 (m, 2 H), 6.34 (t, J = 5.6 Hz, 1 H), 6.71 (d, J = 2.0 Hz, 1 H), 7.00 (dd, J = 8.3, 2.0 Hz, 1 H), 7.24 (d, J = 8.3 Hz, 1 H), 7.32–7.35 (m, 2 H), 7.41–7.45 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 13.7, 19.5, 20.7, 31.1, 42.1, 107.1, 115.9, 120.7, 122.6, 126.8, 130.7, 131.4, 136.4, 138.2, 141.9, 155.1. MS (EI): m/z (%) = 315 (31), 314 (22), 313 (88), 286 (4), 285 (4), 284 (14), 273 (18), 272 (28), 271 (59), 270 (61), 259 (35), 258 (35), 257 (100), 256 (58). HRMS (EI): m/z calcd for C18H20N3 35Cl: 313.1346; found: 313.1351. Compound 7ba: orange solid; mp 183–184 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 0.88 (t, J = 7.4 Hz, 3 H), 1.26–1.35 (m, 2 H), 1.52–1.58 (m, 2 H), 2.41 (s, 3 H), 3.29–3.30 (m, 2 H), 3.64 (s, 3 H), 5.95 (t, J = 5.6 Hz, 1 H), 6.36 (d, J = 2.3 Hz, 1 H), 6.61 (dd, J = 8.4, 2.3 Hz, 1 H), 7.14 (d, J = 8.4 Hz, 1 H), 7.30–7.34 (m, 2 H), 7.41–7.44 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 13.7, 19.5, 20.7, 31.1, 42.2, 55.5, 93.4, 107.8, 115.3, 126.7, 130.6, 132.0, 135.8, 136.9, 137.7, 153.5, 153.9. MS (EI): m/z (%) = 310 (43), 309 (100), 294 (18), 280 (10), 267 (28), 266 (36), 253 (47), 252 (20). HRMS (EI): m/z calcd for C19H23O: 309.1841; found: 309.1834. Compound 7ca: brown crystals; mp 91–93 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 0.85 (t, J = 7.4 Hz, 3 H), 1.25–1.36 (m, 2 H), 1.50–1.57 (m, 2 H), 1.90 (s, 3 H), 3.28–3.34 (m, 2 H), 6.31 (t, J = 5.7 Hz, 1 H), 6.40 (d, J = 2.1 Hz, 1 H), 6.99 (dd, J = 8.3, 2.1 Hz, 1 H), 7.25 (d, J = 8.3 Hz, 1 H), 7.31 (d, J = 7.5 Hz, 2 H), 7.39 (t, J = 7.5 Hz, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 13.7, 17.1, 19.4, 31.2, 41.9, 106.5, 115.9, 120.6, 122.6, 128.8, 129.4, 131.3, 135.1, 137.0, 142.2, 154.8. MS (EI): m/z (%) = 329 (44), 328 (34), 327 (100), 300 (7), 299 (5), 298 (20), 287 (13), 286 (19), 285 (39), 284 (41), 257 (22), 256 (22), 255 (60), 254 (10). HRMS (EI): m/z calcd for C19H22N3 35Cl: 327.1502; found: 327.1503. Compound 7da: brown oil. 1H NMR (500 MHz, DMSO-d 6): δ = 0.89 (t, J = 7.2, 3 H), 1.28–1.36 (m, 2 H), 1.53–1.59 (m, 2 H), 3.26–3.32 (m, 2 H), 6.34–6.39 (m, 2 H), 6.62–6.65 (m, 1 H), 6.80–6.85 (m, 1 H), 7.23 (dd, J = 8.2 Hz, J HF = 4.7 Hz, 1 H), 7.48–7.53 (m, 2 H), 7.66–7.70 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 13.7, 19.5, 31.1, 42.2, 95.0 (d, J CF = 29 Hz), 107.7 (d, J CF = 24 Hz), 115.2 (d, J CF = 9 Hz), 128.9, 130.2, 133.0, 133.2, 135.3 (d, J CF = 13 Hz), 139.3, 154.8, 156.8 (d, J CF = 231 Hz). MS (EI): m/z (%) = 319 (40), 318 (30), 317 (97), 290 (5), 289 (4), 288 (15), 277 (21), 276 (31), 275 (64), 274 (66), 263 (40), 262 (40), 261 (100), 260 (64), 239 (10), 238 (29). HRMS (EI): m/z calcd for C17H17N3 35ClF: 317.1095; found: 317.1096. Compound 7db: colorless crystals; mp 146 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 1.15 (t, J = 7.2 Hz, 3 H), 3.33 (q, overlapped by H2O peak, 2 H), 6.39 (t, J = 5.7 Hz, 1 H), 6.65 (dd, J = 2.5 Hz, J HF = 9.0 Hz, 1 H), 6.83 (ddd, J = 8.5, 2.5 Hz, J HF = 9.0 Hz, 1 H), 7.23 (dd, J = 8.5 Hz, J HF = 4.8 Hz, 1 H), 7.50–7.53 (m, 2 H), 7.66–7.69 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 15.3, 37.8, 95.6 (d, J CF = 28 Hz), 108.2 (d, J CF = 24 Hz), 115.8 (d, J CF = 10 Hz), 129.4, 130.7, 133.4, 133.7, 135.7 (d, J CF = 12 Hz), 139.8, 155.1 (d, J CF = 2 Hz), 157.3 (d, J CF = 231 Hz). MS (EI): m/z (%) = 291 (32), 290 (20), 289 (100), 263 (23), 262 (24), 261 (70), 260 (42), 238 (19), 225 (42). HRMS (EI): m/z calcd for C15H13N3 35ClF: 289.0782; found: 289.0782. Compound 7dc: orange oil. 1H NMR (500 MHz, DMSO-d 6): δ = 1.41 (s, 9 H), 5.57 (s, 1 H), 6.66 (dd, J = 2.5 Hz, J HF = 9.1 Hz, 1 H), 6.84 (ddd, J = 8.6, 2.5 Hz, J HF = 10.1 Hz, 1 H), 7.28 (dd, J = 8.6 Hz, J HF = 4.7 Hz, 1 H), 7.49–7.53 (m, 2 H), 7.65–7.68 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 28.6, 51.5, 95.1 (d, J CF = 28 Hz), 107.8 (d, J CF = 24 Hz), 115.7 (d, J CF = 9 Hz), 128.8, 130.2, 132.7, 133.6, 134.5 (d, J CF = 13 Hz), 139.2, 152.9 (d, J CF = 2 Hz), 157.0 (d, J CF = 232 Hz). MS (EI): m/z (%) = 319 (17), 318 (12), 317 (39), 263 (46), 262 (40), 261 (100), 260 (45), 226 (16), 225 (32). HRMS (EI): m/z calcd for C17H17N3 35ClF: 317.1095; found: 317.1087. Compound 7dd: white solid; mp 164–166 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 6.76 (dd, J = 2.4 Hz, J HF = 8.9 Hz, 1 H), 6.93–6.99 (m, 2 H), 7.27–7.31 (m, 2 H), 7.44 (dd, J = 8.6 Hz, J HF = 4.9 Hz, 1 H), 7.59–7.63 (m, 2 H), 7.69–7.73 (m, 2 H), 7.76–7.79 (m, 2 H), 8.71 (s, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 95.7 (d, J CF = 29 Hz), 108.7 (d, J CF = 24 Hz), 116.9 (d, J CF = 10 Hz), 118.3, 121.3, 128.4, 129.4, 130.3, 133.1, 133.4, 134.6 (d, J CF = 13 Hz), 138.3, 140.5, 150.4, 157.7 (d, J CF = 234 Hz). MS (EI): m/z (%) = 339 (43), 338 (47), 337 (100), 336 (64), 323 (18), 322 (12), 321 (51). HRMS (EI): m/z calcd for C19H13N3 35ClF: 337.0782; found: 337.0786. Compound 7cb: colorless crystals; mp 148–149 °C. 1H NMR (500 MHz, DMSO-d 6): δ = 1.13 (t, J = 7.1 Hz, 3 H), 1.90 (s, 6 H), 3.35 (q, J = 7.1 Hz, 2 H), 6.32 (t, J = 5.7 Hz, 1 H), 6.42 (d, J = 2.2 Hz, 1 H), 7.01 (dd, J = 8.4, 2.2 Hz, 1 H), 7.26 (d, J = 8.4 Hz, 1 H), 7.30–7.33 (m, 2 H), 7.40 (dd, J = 6.9, 8.2 Hz, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 15.0, 17.1, 37.1, 106.6, 116.0, 120.7, 122.7, 128.9, 129.5, 131.3, 135.0, 137.0, 142.2, 154.7. MS (EI): m/z (%) = 301 (35), 300 (23), 299 (100), 284 (19), 271 (20), 257 (18), 256 (17), 255 (49), 228 (23). HRMS (EI): m/z calcd for C17H18N3 35Cl: 299.1189; found: 299.1194. Compound 7ab: yellow oil. 1H NMR (500 MHz, DMSO-d 6): δ = 1.15 (t, J = 7.1 Hz, 3 H), 2.42 (s, 3 H), 3.36 (q, J = 7.1 Hz, 2 H), 6.36 (t, J = 5.6 Hz, 1 H), 6.72 (d, J = 2.2 Hz, 1 H), 7.01 (dd, J = 8.4, 2.2 Hz, 1 H), 7.24 (d, J = 8.4 Hz, 1 H), 7.33–7.36 (m, 2 H), 7.42–7.45 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 14.9, 20.7, 37.3, 107.2, 116.0, 120.8, 122.7, 126.8, 130.7, 131.4, 136.4, 138.2, 141.9, 155.0. MS (EI): m/z (%) = 287 (37), 286 (24), 285 (100), 271 (20), 259 (22), 258 (27), 257 (68), 256 (53), 241 (27). HRMS (EI): m/z calcd for C16H16N3 35Cl: 285.1033; found: 285.1021. Compound 7eb: grey oil. 1H NMR (500 MHz, DMSO-d 6): δ = 1.15 (t, J = 7.1 Hz, 3 H), 2.42 (s, 3 H), 3.35 (q, J = 7.1 Hz, 2 H), 6.38 (t, J = 5.4 Hz, 1 H), 6.84 (d, J = 2.0 Hz, 1 H), 7.12 (dd, J = 8.3, 2.0 Hz, 1 H), 7.20 (d, J = 8.3 Hz, 1 H), 7.33–7.36 (m, 2 H), 7.41–7.45 (m, 2 H). 13C NMR (125 MHz, DMSO-d 6): δ = 15.4, 21.2, 37.8, 110.3, 110.7, 117.1, 124.0, 127.3, 131.2, 131.9, 137.3, 138.7, 142.7, 155.3. MS (EI): m/z (%) = 332 (19), 331 (98), 330 (27), 329 (100), 303 (52), 302 (48), 301 (45), 287 (21), 285 (24). HRMS (EI): m/z calcd for C16H16N3 79Br: 329.0528; found: 329.0530. Compound 7fb: grey oil. 1H NMR (500 MHz, DMSO-d 6): δ = 1.13 (t, J = 7.2 Hz, 3 H), 1.96 (s, 3 H), 3.34 (q, J = 7.2 Hz, 2 H), 6.31 (t, J = 5.5 Hz, 1 H), 6.48 (d, J = 2.0 Hz, 1 H), 7.00 (dd, J = 8.3, 2.0 Hz, 1 H), 7.25 (d, J = 8.3 Hz, 1 H), 7.32–7.35 (m, 1 H), 7.42–7.46 (m, 2 H), 7.50–7.52 (m, 1 H). 13C NMR (125 MHz, DMSO-d 6): δ = 15.0, 17.0, 37.2, 106.9, 115.9, 120.7, 122.6, 127.7, 128.9, 129.7, 131.7, 132.5, 136.2, 136.5, 142.0, 155.1. MS (EI): m/z (%) = 287 (34), 286 (21), 285 (100), 270 (17), 259 (18), 258 (22), 257 (55), 256 (42), 241 (28). HRMS (EI): m/z calcd for C16H16N3 35Cl: 285.1033; found: 285.1032.

      • For recent development, see:
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