Synthesis
General method: 2-Amino-4-nitrophenol (1 eq.) and cyanoguanidine (3 eq.) were dissolved in 1,4-dioxane (30 mL/g 2-amino-4-nitrophenol), followed by the addition of boron trifluoride diethyl ether compound (3.0 eq.). The reaction system was heated under argon protection at 80 °C and the reaction progress was monitored by TLC (5-16 h). Upon completion of the reaction, the reaction mixture was cooled and quenched with saturated aqueous sodium bicarbonate (100 mL/g 2-amino-4-nitrophenol) and subsequently extracted with ethyl acetate (3 x 100 mL). The organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. Depending on the purity of the crude product, the residue can be purified by washing with ethyl acetate, acetone or other suitable organic solvents or by rapid chromatography on silica gel (eluent: cyclohexane/ethyl acetate, gradient from 100/0 to 0/100, v/v) to afford the target product 5-nitrobenzo[d]oxazol-2-amine. The physical properties of the obtained compounds were in agreement with the data reported in the literature.
References
[1] Tetrahedron Letters, 2018, vol. 59, # 17, p. 1642 - 1645
