Cobalt(II)-Catalyzed Oxidative Coupling of Aromatic Tertiary Amines with Enol Silyl Ethers Leading to β-Aminoketone Derivatives

Abstract

We demonstrated that a cobalt(II)-TBHP (tert-butyl hydro­peroxide) oxidizing system efficiently catalyzes the coupling of aromatic tertiary amines with enol silyl ethers, producing the corresponding β-aminoketones.

Key words

cobalt - oxidation - aromatic tertiary amine - enol silyl ether - β-aminoketone

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• 11 General Procedure for a Cobalt-Catalyzed Oxidative Coupling of Aromatic Tertiary Amines with Enol Silyl Ethers To a screw-capped test tube (5 mL) under ambient atmosphere containing freshly distilled MeCN (0.5 mL) were successively added 0.5 M MeCN solution of CoBr₂ (50 μL, 0.025 mmol), aniline (1.0 mmol), enol silyl ether (0.50 mmol), and 5.5 M tert-butyl hydroperoxide in decane (136 μL, 0.750 mmol). After the tube was sealed with a cap that contained a PTFE septum, the mixture was heated at 40 °C (bath temperature) and monitored by GC and TLC analysis. The reaction was quenched with a Na₂CO₃ aq solution (5 mL). The aqueous layer was extracted with CHCl₃, the organic phases were dried over anhydrous Na₂SO₄, filtered, and evaporated under reduced pressure. The crude product was purified by silica chromatography (hexane–EtOAc = 4:1) to give the corresponding β-aminoketone. (3-Methylphenylamino)-1-phenyl-1propanone (1) White solid; 75% (90 mg). ¹H NMR (300 MHz, CDCl₃): δ = 8.00–8.02 (m, 2 H), 7.64–7.51 (m, 3 H), 7.37–7.31 (m, 2 H), 6.85–6.79 (m, 3 H), 3.95–3.90 (t, J = 6.9 Hz, 2 H), 3.34–3.30 (t, J = 6.9 Hz, 2 H), 3.01 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 199.4, 148.5, 136.8, 133.1, 129.3, 128.6, 128.0, 116.5, 112.3, 47.9, 38.5, 35.1. MS (EI): m/z (%) = 239 (100) [M⁺].

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