Opening of N-Tosyl Aziridines with Nucleophiles Catalyzed by Phosphomolybdic Acid Supported on Silica Gel

Abstract

An environmentally benign H₃PMo₁₂O₄₀-SiO₂-catalyzed regioselective opening of activated aziridines with alcohols, azide, cyanide and bromide, at ambient temperature to afford the corresponding β-amino derivatives in good yields is described.

Key words

phosphomolybdic acid - silica gel - aziridines - regioselectivity - alcoholysis - β-amino ether - β-azido amine - β-cyano amine - β-bromo amine

References

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• Experimental Procedure.
• 15a

  Preparation of PMA-SiO ₂ Catalyst (10% by wt): To a solution of H₃PMo₁₂O₄₀ (0.1 equiv) in MeOH, silica gel (0.9 equiv) (100-200 mesh) was added slowly and stirred at r.t. for about 6 h and MeOH was removed under reduced pressure, which yielded PMA-SiO₂ as a yellow solid.

• 15b Preparation of β-Amino Ethers: A mixture of N-tosyl aziridine (1 mmol), alcohol (see Table 1) and PMA-SiO₂ (0.01 mmol, based on PMA) in MeCN (3 mL) was stirred at r.t. for appropriate time (see Table 1). After completion of the reaction, as indicated by TLC, the solvent was removed under reduced pressure and the residue was dissolved in THF and filtered. The filtrate was concentrated under reduced pressure and purified by column chromatography on silica gel (100-200 mesh) to afford pure β-amino ethers
• 15c

  Preparation of β-Azido-, Cyano- and Bromo Amines: A mixture of N-tosyl aziridine (1 mmol), NaN₃, NaCN or KBr (1.1 mmol) and PMA-SiO₂ (0.01 mmol, based on PMA) in MeCN and H₂O (3 mL, 9: 1) was stirred at r.t. for an appropriate time (see Table [2] ). After completion of the reaction, as indicated by TLC, the reaction mixture was filtered and the filtrate was concentrated and purified by column chromatography on silica gel (100-200 mesh) to afford pure β-azido-, cyano- or bromo amines.
  Spectral Data for Selected Products: Table 1, Entry 9: IR (neat): 3472, 3287, 2930, 1600, 1403, 1323, 1155, 1086 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.74 (d, J = 8.1 Hz, 2 H), 7.73-7.18 (m, 7 H), 5.53 (d, J = 8.4 Hz, 1 H, NH), 4.35 (d, J = 3.5 Hz, 1 H), 3.74 (dd, J = 11.6 and 3.1 Hz, 1 H), 3.37-3.34 (m, 1 H), 3.27-3.19 (m, 4 H), 2.43-2.40 (m, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 143.5, 137.6, 137.3, 129.7, 128.7, 128.1, 127.0, 126.4, 86.1, 60.5, 58.8, 58.0, 21.5. MS (EI, 70 eV): m/z = 335 (1.5) [M⁺ + 1], 304 (1.2), 155 (20), 121 (100), 91 (60).
  Table 1, Entry 10: IR (neat): 3396, 2976, 1734, 1600, 1440, 1366, 1321, 1244, 1152, 1091, 1033, 953, 880, 812, 659 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.67 (d, J = 8.0 Hz, 2 H), 7.21 (d, J = 7.4 Hz, 2 H), 4.69-4.60 (m, 2 H), 3.17-3.12 (m, 1 H), 2.99 (s, 3 H), 2.34 (s, 3 H), 1.91 (s, 3 H), 1.61-1.18 (m, 5 H), 1.02-0.94 (m, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 170.7, 142.8, 139.2, 129.4, 126.9, 71.1, 62.1, 49.1, 32.9, 26.6, 22.2, 21.9, 21.4, 21.3, 20.0, 19.8. MS (EI, 70 eV): m/z = 298 (0.5) [M⁺ - C₄H₉O], 216 (10), 155 (15), 73 (100). Table 2, Entry 8: IR (KBr): 3488, 3136, 2096, 1603, 1446, 1328, 1283, 1260, 1155, 1078, 1040, 956, 806, 755, 694 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.59 (d, J = 8.2 Hz, 2 H), 7.27-7.14 (m, 7 H), 5.55 (d, J = 8.0 Hz, 1 H, NH), 4.75 (d, J = 6.2 Hz, 1 H), 3.77-3.74 (m, 1 H), 3.54-3.42 (m, 2 H), 2.61 (br s, OH), 2.40 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 143.6, 136.9, 135.8, 129.7, 128.9, 128.5, 127.1, 126.9, 66.5, 60.6, 58.6, 21.5. MS (EI, 70 eV): m/z = 347 (6) [M⁺ + 1], 301 (100), 274 (45), 145 (98).