prepare 4-bromopyridine from pyridine Noxide
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Answer:
4-(4-Dimethyl aminophenyl)ethynylpyridine 476 (R = 4-NMe2)410
4-Bromopyridine hydrochloride 106 (1.94 g; 10 m mol), the palladium catalyst (140 mg; 2 mol%), and CuI (20 mg, 1 mol%) were placed in a flask and degassed. To the reaction flask was added piperidine (0.3 mL) or TEA (0.2 mL). The acetylene 475 (R = 4-NMe2) was added to the reaction mixture in CH3CN (previously purged with N2 + H2) at about 80 °C. The reaction was stirred at reflux for 8 h under the reducing atmosphere. After the base workup followed by silica gel chromatography, the by-product bis (4-N,N-dimethyl aminophenyl)butadiyne (58 mg) and the cross-coupled product 476 (R = 4-NMe2) (2.1 g, 94%) were isolated. 1H NMR (CDCl3 400 Hz): δ (ppm) = 8.52 (d, J = 6.1 Hz, 2H); 7.40 (d, J = 9.0 Hz, 2H); 7.31 (d, J = 6.1 Hz, 2H); 6.64 (d, J = 9.0 Hz, 2H); 2.99 (s, 6H).