A Convenient Procedure for the Oxidative Dehydrogenation of N-Heterocycles Catalyzed by FeCl₂/DMSO

Abstract

A convenient catalytic procedure has been developed for the oxidative dehydrogenations of N-heterocycles. Combining catalytic FeCl₂ with DMSO yields a catalyst that promotes the dehydrogenation of tetrahydroquinolines and related heterocycles under 1 bar of O₂, affording the corresponding N-heteroaromatic products in moderate yields.

Key words

oxidative dehydrogenation - N-heterocycle - iron catalyst - DMSO - quinolines

• References and Notes

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• 20 Typical Procedure To a Schlenk tube equipped with a magnetic stir bar were added 8-methyl-1,2,3,4-tetrohydroquinoline (0.50 mmol), FeCl₂ (1.9 mg, 1.5·10^–2 mmol), DMSO (31.2 mg, 0.4 mmol), and p-xylene (1 mL). The reaction mixture was stirred at 110 °C under an oxygen atmosphere using a balloon and monitored by TLC. After the reaction, the mixture was cooled to room temperature and purified using flash chromatography (hexane–EtOAc, 10:1) to give the corresponding product 8-methylquinoline in 70% yield. 8-Methylquinoline Colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.93 (m, 1 H), 8.10 (m, 1 H), 7.64 (d, J = 4.0 Hz, 1 H), 7.54 (m, 1 H), 7.43–7.35 (m, 2 H) 2.82 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 149.2, 147.3, 137.1, 136.3, 129.6, 128.3, 126.3, 125.9, 120.8, 18.2. HRMS: m/z calcd for [C₁₀H₉N + H⁺]: 144.0813; found: 144.0813.