Efficient Synthesis of N-(9-Xanthyl)-4-Toluenesulfonamides Enabled by an Addition–Cyclization Cascade of Arynes

Abstract

An efficient synthesis of N-(9-xanthyl)-4-toluenesulfonamides is described in which salicyl N-tosylimines react with silyl­aryl triflates in the presence of CsF. This mild process involves an addition–cyclization cascade in which arynes are generated and trapped in situ.

Key words

N-(9-xanthyl)-4-toluenesulfonamides - salicyl N-tosyl­imines - arynes - addition–cyclization - cascade

• References and Notes


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• 10 General Procedure for the Preparation of N-(9-Xanthyl)-4-Toluenesulfonamides Synthesized from Salicyl N-Tosylimines and 2-(Trimethylsilyl)aryl Triflates To a solution of salicyl N-tosylimine¹¹ (0.38 mmol, 1.0 equiv) and triflate (0.49 mmol, 1.3 equiv) in MeCN (5 mL) was added CsF (0.95 mmol, 2.5 equiv) in one portion. After stirring at r.t. for the indicated time (Table 2), the reaction mixture was poured into 10% aq Na₂CO₃ (5 mL). The resulting mixture was extracted with EtOAc (3 × 5 mL). The combined extracts were dried over Na₂SO₄, filtered, and evaporated to give a crude product, which was purified by silica gel column chromatography using elution with EtOAc–PE to afford N-(9-xanthyl)-4-toluenesulfonamide. The general procedure was followed using salicyl N-tosyl-imine (2a, 105 mg, 0.38 mmol), silylaryl triflate 1a (146 mg, 0.49 mmol), and CsF (144 mg, 0.95 mmol). The reaction mixture was stirred for 6 h and purified by silica gel chromatography using PE–EtOAc (5:1) as eluent to give cyclization product 3a (122 mg, 92% yield) as a white solid; mp 196–198 °C (lit.⁹ mp 197–197.5 °C). ¹H NMR (400 MHz, CDCl₃): δ = 7.80 (d, J = 8.1 Hz, 2 H), 7.37–7.20 (m, 4 H), 7.15 (d, J = 7.8 Hz, 2 H), 7.08 (d, J = 8.2 Hz, 2 H), 6.99 (t, J = 7.5 Hz, 2 H), 5.77 (d, J = 8.6 Hz, 1 H), 4.87 (d, J = 8.6 Hz, 1 H), 2.47 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 151.5, 143.8, 138.8, 130.0, 129.7 (overlap, 2 C), 127.4, 123.8, 120.6, 116.9, 49.4, 21.8. ESI-HRMS: m/z calcd for C₂₀H₁₇NO₃SNa [M + Na]⁺: 374.0821; found: 374.0825. See the Supporting Information for experimental details and characterization data for all new compounds.
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