Sulfonoketenimides as Key Intermediates for the Synthesis of N-Tosyl-acetoyloxy Alkanimines

Abstract

A copper-catalyzed multicomponent reaction between terminal alkynes, sulfonyl azides, and oximes for the synthesis of N-tosylacetoyloxy alkanimines is reported. This one-pot procedure is carried out in the presence of copper(I) iodide in acetonitrile at room temperature.

Key words

alkanimines - terminal alkyne - sulfonyl azide - oxime - copper iodide

• References and Notes

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• 15 Typical Procedure for the Preparation of Products 4a–i To a stirred solution of alkyne (1, 1.0 mmol), sulfonylazide (2, 1.0 mmol), and CuI (19 mg, 0.10 mmol) in MeCN (2 mL) was added Et₃N (1.5 mL) under argon at r.t. After 10 min, oxime (3, 1.2 mmol) was added, and the mixture was stirred for 4 h. The solvent was removed, the residue treated with of sat. aq NH₄Cl (3 mL) and extracted with EtOAc (3 × 5 mL). Organic layers were combined, dried over anhydrous Na₂SO₄, and concentrated under vacuum. The residue was purified by chromatography (silica gel, hexane–EtOAc = 2:1) to give 4. 4-Methyl-N-[(-phenylmethyleneaminooxy)phenyl-ethylidene]benzenesulfonamide (4a) Colorless solid, mp 156–158 °C; yield 0.34 g (87%). IR (KBr): ν_max = 3020, 2972, 1569, 1528, 1335, 1128 cm^–1. ¹H NMR (500.1 MHz, CDCl₃): δ = 2.44 (3 H, s, CH₃), 3.60 (2 H, s, CH₂), 7.14 (2 H, d, ³ J = 8.9 Hz, 2 CH), 7.31–7.48 (8 H, m, 8 CH), 7.82 (2 H, ³ J = 8.5 Hz, 2 CH), 7.88 (2 H, d, ³ J = 8.2 Hz, 2 CH), 7.97 (1 H, s, CH). ¹³C NMR (125.7 MHz, CDCl₃): δ = 21.7 (CH₃), 43.8 (CH₂), 126.1 (2 CH), 128.1 (CH), 128.5 (2 CH), 128.8 (2 CH), 129.0 (2 CH), 129.3 (CH), 129.4 (2 CH), 129.6 (2 CH), 133.7 (C), 137.5 (C), 141.0 (C), 143.2 (CH), 154.5 (CH), 165.9 (C). MS (EI): m/z (%) = 392 (5) [M⁺], 271 (13), 251 (100), 140 (10), 104 (14), 77 (60), 76 (42), 64 (44). Anal. Calcd (%) for C₂₂H₂₀N₂O₃S (392.47): C, 67.33; H, 5.14; N, 7.14. Found: C, 67.75; H, 5.19; N, 7.21.
• 16a Conversion of 4a into 2-Phenyl-N-tosylacetamide (5) To a stirred solution of 4a (1 mmol) in MeOH (3 mL) was added NH₄Cl (1 mmol) in H₂O (1 mL). Then, Zn powder (2 mmol) was added, and the mixture was heated at 70 °C for 2 h. The mixture was cooled, filtered, and the filtrate was extracted with EtOAc. The organic layer was evaporated and purified by chromatography (silica gel, hexane–EtOAc = 3:1) to give 5.
• 16b Cassidy MP, Raushel J, Fokin VV. Angew. Chem. Int. Ed. 2006; 45: 3154