Synthesis
A tetrahydrofuran (26 mL) solution of methyl lithium (1.3 M, 33.80 mmol) was slowly added dropwise to an ethyl ether (100 mL) solution of 2,2'-bipyridine (5.30 g, 34.00 mmol) at 0°C and under nitrogen protection. The reaction mixture was stirred at this temperature for 2 hours and then refluxed at elevated temperature for 3 hours. When the reaction solution was cooled to room temperature, the reaction was quenched by the addition of water (10 mL). The organic phase was separated and the aqueous phase was extracted with ether three times. The organic phases were combined and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure to give an orange colored oil. This oily material was dissolved in acetone solution saturated with potassium permanganate (300 mL) and stirred at room temperature for 1 hour for oxidation reaction. The filtrate was filtered and concentrated to remove the acetone. The residue was purified by vacuum distillation to afford the colorless oily target product 6-methyl-2,2'-bipyridine (3.73 g, 63.8% yield). The structure of the product was confirmed by nuclear magnetic resonance hydrogen spectroscopy (1H NMR, 400MHz, CDCl3), carbon spectroscopy (13C NMR, 100MHz, CDCl3) and electrospray ionization mass spectrometry (ESI-MS): 1H NMR δ 8.65 (s, 1H), 8.38 (d, J = 8.0 Hz, 1H), 8.15 (d, J = 7.9 Hz, 1H), 7.72-7.82 (d, J = 7.9 Hz, 1H), 8.15 (d, J = 7.9 Hz, 1H) 7.72-7.82 (m, 1H), 7.66 (d, J = 7.7 Hz, 1H), 7.21-7.30 (m, 1H), 7.13 (d, J = 7.7 Hz, 1H), 2.61 (s, 3H); 13C NMR δ 157.7, 156.3, 155.4, 149.0, 136.9, 136.7, 123.6, 123.2, 121.02, 117.9, 24.5; ESI-MS m/z: [M+H]+ measured value 171.61 (calculated value 171.22).
References
[1] Angewandte Chemie - International Edition, 2014, vol. 53, # 23, p. 5872 - 5876
[2] Dyes and Pigments, 2016, vol. 128, p. 33 - 40
[3] Patent: CN105669689, 2016, A. Location in patent: Paragraph 0032
[4] Angewandte Chemie - International Edition, 2016, vol. 55, # 37, p. 11207 - 11211
[5] Angew. Chem., 2016, vol. 128, # 37, p. 11373 - 11377,5
