Highly Regioselective Route to Substituted Imidazo[1,2-a]quinoxalines

A new synthesis of unsymmetrically substituted imidazo[1,2-a]quinoxalines via regioselective displacement of 3-chloro group in 2-(methylthio)-3-chloroquinoxalines by aminoacetaldehyde dimethylacetal and subsequent-acid mediated intramolecular cyclization of the resulting adducts is reported in this study. The utility of the 3-(methylthio) group in these imidazoquinoxalines is also demonstrated by conversion of one of the 2-(methylthio)quinoxalines to 2-(methylsulfonyl) derivative and its subsequent displacement by hydroxy-, phenoxy- and n-butylamino groups, thus affording various 2-substituted imidazo[1,2-a]quinoxalines.