Cascade Synthesis of Benzothieno[3,2-b]indoles under Oxidative Conditions Mediated by CuBr and tert-Butyl Hydroperoxide

A series of biologically relevant compounds of benzothieno[3,2-b]indole derivatives were conveniently synthesized from reactions of N-protected 2-((2-bromophenyl)ethynyl)anilines and potassium ethylxanthate, mediated by cuprous bromide/tert-butyl hydroperoxide. The method features the construction of the pyrrole and thiophene rings in a cascade sequence with the pyrrole ring being formed prior to the thiophene ring via a possible reactive Cu(III)-pyrrole intermediate.