Synthesis of thieno[2,3-b]quinoxalines and pyrrolo[1,2-a]quinoxalines from 2-haloquinoxalines

Abstract

The palladium(0)-catalysed coupling of 2-haloquinoxalines with functionally substituted alkynes, addition of one mol equivalent of bromine to the 2-alkynylquinoxalines thus produced and then reaction of the resulting dibromides with disodium trithiocarbonate produced 2-hydroxymethyl- and 2-(diethoxymethyl)thieno[2,3-b]quinoxalines. Addition of bromine to some 6-substituted-2-(3,3-diethoxypropyn-1-yl)quinoxalines gave pyrrolo[1,2-a]quinoxalines. Treatment of a 3-(1,2-dibromoalkenyl)quinoline, a 3-(1,2-dibromoalkenyl)pyrazine, and a 5-(1,2-dibromoalkenyl)pyrimidine with disodium trithiocarbonate failed to induce thiophene ring formation.