1-Ethynyl-4-methoxybenzene → 2-(4-Methoxy phenylethynyl)pyridine-3-carboxaldehyde

Participants

Reaction Conditions

Reaction Steps

To a solution of 2-bromo-3-pyridinecarboxaldehyde (1.86 g, 10 mmol) and 4′-methoxy phenylacetylene (1.58 g, 12 mmol) in triethylamine (40 mL) were added dichlorobis(triphenylphosphine) palladium(II) (140 mg, 2 mol %) and copper (I) iodide (20 mg, 1 mol %). The reaction mixture was heated at 50° C. under nitrogen for 3 h, then cooled to room temperature. The ammonium salt was removed by filtration. The filtrate was concentrated under reduced pressure leaving 2-(4-methoxy phenylethynyl)pyridine-3-carboxaldehyde (2.35 g, 99%) as yellow solid. 2-(4-Methoxyphenylethynyl)pyridine-3-carboxaldehyde (2.28 g, 9.60 mmol) and tert-butylamine (3.83 g, 60 mmol) were stirred under nitrogen for 24 h at rt. The resulting mixture was extracted with ether and dried over anhydrous Na2SO4. Removal of solvent gave the imine (2.72 g, 97%) which was used in next step without further purification. To a solution of this imine (2.7 g, 9.23 mmol) in 50 mL anhydrous DMF was added (0.190 g, 0.1 mmol) copper (I) iodide. The reaction mixture was heated at 100° C. for 4 h, then cooled to room temperature and diluted with ether (200 mL). The organic layer was washed with sat. aqueous ammonium chloride solution (3×100 mL). The organic layer was dried over anhydrous Na2SO4. Removal of solvent gave the crude compound as a dark colored solid. Purification by column chromatography (Silica Gel 230-400 mesh; 30% ethyl acetate in hexanes as eluent) afforded 7-(4-methoxy phenyl) [1,6]naphthridine (0.730 g, 33%) as a brown solid. To a solution of 7-(4-methoxy phenyl) [1,6]naphthridine (0.485 g, 2.05 mmol) in anhydrous N-methyl-2-pyrrolidinone (5 mL) was added thiophenol (0.25 g, 2.26 mmol) and potassium carbonate (0.028 g, 0.205 mmol). The reaction mixture was stirred at 190° C. for 1 h under nitrogen. The reaction mixture was cooled to room temperature. The crude compound was adsorbed onto silica gel and purified by column chromatography (Silica Gel 230-400 mesh; 20-70% ethyl acetate in hexanes as fluent) to give 4-(1,6-naphthyridin-7-yl)phenol (0.33 g, 71%) as a pale yellow solid. MS (ES) m/z: 223.95 (M+1), 222.95 (M); Mp. 219-221° C.

Provenance & Evidence