One-pot approach to construct benzo[4,5]thieno[3,2-b]indoles, pyrido[3′,2’:4,5]thieno[3,2-b]indoles and pyrazino[2′,3’:4,5]thieno[3,2-b]indoles based on the Fischer indole synthesis

During this study, series of benzo[4,5]thieno[3,2-b]indoles, pyrido[3′,2’:4,5]thieno[3,2-b]indoles and pyrazino[2′,3’:4,5]thieno[3,2-b]indoles were efficiently synthesized from benzo- and pyrido- or pyrazino-fused 3-aminothiophene-2-carboxylates, respectively, using one-pot two-step strategy based on the Fischer indolization reaction. The essence of this synthetic approach is acid-promoted reaction of the 3-aminothiophene intermediates, in situ generated from the corresponding ring-fused 3-aminothiophene-2-carboxylates, with arylhydrazines to give arylhydrazones of thiophen-3(2H)-ones, followed by their indolization to afford thieno[3,2-b]indole-cored molecules.