Further investigation of quinoxalines, synthesis and characterization

ABSTRACT

A convenient route is described for the preparation of s-triazolo [4, 3 - a] quinoxalines through the condensation reaction of 2 -chloro-3- hydrazino quinoxaline [I] with different aromatic aldehydes to afford the corresponding hydrazones [II]. 4- Chloro-1- aryl-1, 2, 4 -triazolo [4, 3 - a] quinoxalines [III] were prepared by the cyclization of [II] with bromine / acetic acid. The very reactive 4 chloro substituent was displaced by a variety of nucleophiles to yield 4 alkoxy [IV], or 4 - substituted amino - [V], or 4-diethyl malonyl ester [VI] of the 1 -aryl - 1, 2, 4 - triazolo [4, 3 - a] quinoxalines. Reaction of [VI] with phenyl hydrazine afforded 1 aryl 4 [1 - phenyl - 3,/ 5 - dioxo-pyrazolidin- 4-yl] 1,2,4-triazolo. [4, 3 - a] quinoxaline [VII]. The isolated ring system in which quinoxaline is incorporated with pyrazolinone [VIII] was achieved via the reaction of [I] with ethyl 2-methyl acetoacetate, then it was allowed to react with sodium methoxide to yield the 2 - methoxy - 3 -[3, 4 - dimethyl - 5 -oxo-pyrazolin - 1 - yl] quinoxaline [IX]. In addition, 2,3 - dichloroquinoxaline [C] was allowed to react with o - aminoacetophenone to give 2 - chloro - 3 - [0 - acetylanilino]-quinoxaline [X]