C- vs. N-Oxidations of Benzyltriazanes: Selective Access to Triazones, Azimines, and Triazenes

Abstract

The oxidation of several benzyltriazanes has been studied. Routes to the selective formation of triazenes, azimines, and triazones via C- or N-oxidation (and rearrangement) were devised. The rich reactivity of triazanes shows that trinitrogen chains are interesting functions, whose reactivity has been overlooked despite their interest as 3-N building blocks.

Key words

hydrazines - hypervalent iodine - oxidation - azimines - ­triazanes

• References and Notes

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Triazenes are important compounds with a rich reactivity, see:
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• 12 General Procedure for the Formation of Triazones The triazane (0.5 mmol) was dissolved in CH₂Cl₂ (4 mL) under N₂ at rt K₂CO₃ (10 equiv) and lead(IV) acetate (1 equiv, 85%) were added at –78 °C. The cold bath was removed, and the reaction mixture was stirred for 30 min. The precipitate was filtered off and washed several times with CH₂Cl₂. The combined organics extracts were concentrated in vacuo and purified by column chromatography. Compound 2a: ¹H NMR (400 MHz, CDCl₃) δ: 1.50 and 1.58 (bs + s, 18H, t-Bu), 6.45 (s, 1H, NH), 7.35–7.39 (m, 3H, Ar), 7.71–7.75 (m, 2H, Ar), 7.92 (s, 1H, CH=N). ¹³C NMR (100 MHz, CDCl₃) δ: 28.0 (Me), 82.3 (C-N), 82.9 (C-N), 127.6 (CH), 128.4 (CH), 129.6 (CH), 134.0 (C), 139.5 (CH=N), 151.6 (C=O), 153.8 (C=O). ESI-HRMS: m/z calcd [M+H]⁺: 336.1918; found: 336.1924 (1.8 ppm). IR (neat): ν = 1450, 1479, 1720, 2979, 3287 cm^–1; mp 106°C, decomp: 159°C. General Procedure for the Formation of Triazenes or Azimines The triazane (0.5 mmol) was dissolved in EtOH (10 mL) under N₂ at rt PhI(OAc)₂ (2.2 equiv) was added at 0 °C, and the reaction mixture was stirred for 30 min at 0 °C. Water was then added, and the mixture was extracted three times with EtOAc. The combined organic extracts were washed with water and brine, dried over MgSO₄, filtered, and the solvent removed. The tri­azenes (or azimine) were purified by chromatography. Compound 5: ¹H NMR (400 MHz, CDCl₃): δ = 1.52 (s, 18 H, ­t-Bu), 5.50 (s, CH₂), 7.36–7.38 (m, 3 H, Ar), 7.48–7.51 (m, 2H, Ar). ¹³C NMR (100 MHz, CDCl₃): δ = 28.2 (Me, t-Bu), 74.3 (CH₂), 82.8 (C, t-Bu), 128.8 (CH, Ar), 129.0 (CH, Ar), 129.2 (CH, Ar), 132.3 (C, Ar), 156.7 (C=O). ESI-HRMS: m/z calcd [M + Na]⁺: 358.1737; found: 358.1720 (4.8 ppm). IR (neat): ν = 1467, 1690, 1704, 2927, 2975 cm^–1; mp 145–146 °C, decomp.: 150 °C.