[Synthesis]
A mixture of 2-amino-3-chloroquinoxaline (495 mg, 2.75 mmol) and diphenylphosphine (0.48 mL, 2.76 mmol) was heated and reacted at 130 °C for 2 h under the catalytic influence of Pd(OAc)2 (0.8 mg, 0.13 mmol) to give a viscous blue-green product. The reaction mixture was extracted with diethyl ether and the soluble fraction was monitored by NMR in C6D6 to identify tetraphenyl diphenylphosphine (Ph2P-PPh2), diphenylchlorophosphine (Ph2PCl), 2-aminoquinoxaline (3a), and an unknown phosphorus compound (31P NMR signals: δ 14.9, 82.2, 12.8, 5.4 ppm, intensity ratio 84:12:2:2). The ether-insoluble hydrochloride fraction was treated with aqueous NaOH/Et2O to give 615 mg of blue-green powder. The ether phase was dried over Na2SO4 and the ether was removed under reduced pressure to give 220 mg of a brownish-yellow viscous substance with a low content of 2-aminoquinoxaline (about 20% relative intensity of 31P in addition to signals from tetraphenyldiphosphine, diphenyloxyphosphine and other phosphorus compounds). The mixture was purified by silica gel column chromatography (ethyl acetate/hexane, 95/5%) under aerobic conditions, and removal of the solvent afforded 180 mg (45% yield) of 2-aminoquinoxaline as a light yellow solid, with a melting point of 156 °C.1H NMR (CDCl3) δ: 5.03 (vbr, 2H, NH2), 7.45 (td, 3J = 8.4, 7, 4J = 1.2 Hz, 1H, H-6), 7.61 (td, 3J = 8.4, 7, 4J = 1.2 Hz, 1H, H-7), 7.67 (dd, 3J = 8.4, 4J = 1.2 Hz, 1H, H-8), 7.92 (dd, 3J = 8.4, 4J = 1.2 Hz, 1H, H-5), 8.35 (s, 1H, H-3); these data are in agreement with the literature [17]. literature [17].13C NMR (CDCl3) δ: 125.05 (CH-6), 125.88 (CH-8), 128.83 (CH-5), 137.43 (Cq-4a), 137.78 (CH-3), 130.29 (CH-7), 140.89 (Cq-8a), 151.97 (Cq-2). HRMS (ESI in MeOH): calculated value C8H7N3 [M+H]+ 146.0713; measured value: 146.0713. |