Domino Reactions of Thiopyrano[4,3-B]Indole-3(5h)-Thiones and Dimethyl Acetylenedicarboxylate: Quantum Chemical and Experimental Data

Reaction of thiopyrano[4,3- b ]indole-3(5 H )-thiones and dimethyl acetylenedicarboxylate proceed via two competing cascade pathways. Both mechanisms have been investigated in detail by DFT PCM/B3LYP/6-311++G(d,p) quantum chemical calculations. Initially, the reactions occur via an alkyne–thiocarbonyl metathesis or (3+2) cycloaddition mechanisms. At the next stages, two parallel rearrangements in both cases proceed, including thiopyrane rings opening and thiophene rings closure. Cycloaddition processes of intermediate thioketones and a second equivalent of DMAD leads to the resulting thiopyrano[4,3- b ]indole derivatives bearing thienyl substituent.