General procedure for the synthesis of oxazolo[4,5-b]pyridines from 2-amino-3-hydroxypyridine (90.1 mmol) and triethyl orthoformate (720.7 mmol): 2-amino-3-hydroxypyridine was dissolved in triethyl orthoformate under nitrogen protection, and p-toluenesulfonic acid (4.50 mmol) was added as catalyst. The reaction mixture was stirred at 160 °C overnight. Upon completion of the reaction, the excess of triethyl orthoformate was removed by distillation under reduced pressure. The crude product was purified by column chromatography with the eluent cyclohexane/ethyl acetate (5%-40% gradient elution) to afford oxazolo[4,5-b]pyridine as a beige solid in 68% yield. The product was detected by mass spectrometry (LRMS) with [M + H]+ m/z of 121.1; 1H NMR (DMSO-d6, 400 MHz) δ 9.04 (s, 1H), 8.58 (dd, J = 4.8, 1.4 Hz, 1H), 8.26 (dd, J = 8.2, 1.4 Hz, 1H), 7.50 (dd, J = 8.2, 4.8 Hz , 1H), 6.41 (s, 2H); 13C NMR (DMSO-d6, 101 MHz) δ 157.7, 154.5, 147.1, 142.0, 121.5, 120.1.
![Oxazolo[4,5-b]pyridine](/CAS/GIF/273-97-2.gif)