Amides and Ethers as Chemoselective Surrogates for Copper(II)-Catalyzed ortho Benzoyloxylation of 2-Phenylpyridines

Abstract

Chemoselective ortho benzoyloxylation of 2-phenylpyridine derivatives using amides and ethers as novel arylcarboxy sources using a Cu(II)/TBHP catalytic system has been reported. It is a simple protocol for ortho benzoyloxylation using amides and ethers as surrogates. A broad range of amides and ethers was found to be compatible under optimized reaction conditions to provide the corresponding products in good to excellent yield. The reaction proceeds through the cleavage of C–N, C–O, and C–H bonds and the formation of a new C–O bond via C–H functionalization.

Key words

C–H activation - amide - ether - copper acetate - benzoyloxylation

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• 14 Representative Experimental Procedure for the Oxidative Benzoyloxylation of 2-Phenylpyridine with N-Methoxybenzamide 2-Phenylpyridine (1a, 0.5 mmol, 77 mg), o-methoxybenzamide (2a, 0.5 mmol, 75 mg), and Cu(OAc)₂ (5 mol%, 18 mg) in chlorobenzene (0.5 mL) were charged in an oven-dried 10 mL single-necked round-bottom flask. At r.t. TBHP (5–6 M in decane, 5 mmol. 0.5 mL) was added dropwise to the reaction flask with stirring. The flask was then equipped with a condenser, and the reaction mixture was stirred at 120 °C for 24 h open to the atmosphere, and the progress of reaction was monitored by TLC and/or GC. After completion, the reaction mixture was allowed to cool to r.t., diluted with EtOAc (10 mL), and the organic phase was washed with 5% aq NaHCO₃ (2 × 5 mL) followed by H₂O (2 × 5 mL). The organic phase was dried over Na₂SO₄, filtered, and the solvent was evaporated by rotary evaporation to obtain the crude product that was then purified by column chromatography (silica gel, 100–200 mesh), with PE–EtOAc as the eluent to afford the pure product. The products structure and purity were confirmed by GC–MS spectrometry and ¹H and ¹³C NMR spectroscopic analysis. Representative Analytical Data 2-(Pyridin-2-yl)phenyl 4-Methylbenzoate (3ab) ¹⁰ Yield: 114 mg (79%); yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.59 (d, J = 4 Hz, 1 H), 7.95 (d, J = 8 Hz, 2 H), 7.78–7.75 (m, 1 H), 7.60–7.58 (m, 1 H), 7.54 (d, J = 8 Hz, 1 H), 7.46–7.44 (m, 1 H), 7.40–7.36 (m, 1 H), 7.29–7.23 (m, 3 H), 7.16–7.13 (m, 1 H), 2.41 (s, 3 H) ppm. ¹³C NMR (125 MHz, CDCl₃): δ = 165.21, 155.55, 149.62, 148.33, 144.31, 136.13, 133.34, 130.92, 130.24, 129.71, 129.23, 126.69, 126.33, 123.77, 123.37, 122.12, 21.76 ppm. GC–MS (EI, 70 eV): m/z (%) = 289 (10.3) [M⁺], 119 (100), 91 (28.6), 65 (8.7), 40 (31.0).