Highly Efficient Copper-Catalyzed O-Arylation Using Readily Available (S)-N-Methylpyrrolidine-2-Carboxamide as the Ligand

Abstract

A highly efficient and readily available catalyst system for O-arylation of various phenols using CuI and (S)-N-methylpyrrolidine-2-carboxamide (Pro-NHMe) was developed. The reaction is widely applicable to the synthesis of diaryl ethers

Key words

Ullmann reaction - O-arylation - cross-coupling - copper-catalyzed - N,N-ligand

References and Notes

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16

General Procedure for the Preparation of Compounds 3a-m: Aryl halide (2 mmol for entries 1-8 and 10-14, 1 mmol for entry 9 in Table [1] ), substituted phenol (3 mmol) and (S)-N-methylpyrrolidine-2-carboxamide hydrochloride (66 mg, 0.4 mmol) were added to a flask with potassium phosphate (607 mg, 4.4 mmol) and DMF containing 3% H₂O (3 mL), and the mixture was stirred for 30 min at r.t. Under a nitrogen atmosphere CuI (40 mg, 0.2 mmol) was added to the flask. The flask was immersed in an oil bath, and the reaction mixture was stirred at 110 °C for the reaction time shown in Table [1] . The reaction mixture was then allowed to cool to r.t., diluted with EtOAc (10 mL) and filtered, and the filtrate was concentrated under vacuum to give the crude product. Purification by column chromatography on silica gel (hexane-EtOAc, 15:1 → 50:1) afforded the desired pure product.
1-Methoxy-4- o -tolyloxybenzene (3d):¹⁷ colorless oil. ¹H NMR (300 MHz, CDCl₃): δ = 7.18 (m, 1 H), 7.07 (m, 1 H), 6.97 (m, 1 H), 6.79 (m, 5 H), 3.73 (s, 3 H), 2.26 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 156.03, 155.51, 151.26, 131.49, 129.21, 127.18, 123.28, 119.53, 118.18, 114.98, 55.76, 16.42. HRMS (EI): m/z [M⁺] calcd for C₁₄H₁₄O₂: 214.0994; found: 214.0986.
1-Bromo-4-(4-methoxyphenoxy)benzene (3g): white solid; mp 84-86 °C. ¹H NMR (300 MHz, CDCl₃): δ = 7.36 (d, J = 8.25 Hz, 2 H), 6.86-6.97 (dd, J = 8.94, 25.08 Hz, 4 H), 6.80 (d, J = 8.91 Hz, 2 H), 3.79 (s, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 157.9, 156.3, 149.7, 132.6, 121.0, 119.3, 115.1, 114.8, 55.7. HRMS (EI): m/z [M⁺] calcd for C₁₃H₁₁BrO₂: 277.9942; found: 277.9948.