Reaction of thiopyrano[4,3-b]indole-3(5H)-thiones and dimethyl acetylenedicarboxylate (DMAD) proceeds via two competing cascade pathways. Initially, both the pathways begin from thiocarbonyl sulfur and acetylene carbon atoms interaction. Then two parallel processes take place: an alkyne–thiocarbonyl metathesis and a (3 + 2) cycloaddition. In the next stages, in both cases, thiophene ring formation and thiopyran ring opening proceed. Finally, (4 + 2) cycloaddition reactions of intermediate thioketones and a second equivalent of DMAD leads to the resulting thiopyrano[4,3-b]indole derivatives bearing thienyl substituent. The kinetic and thermodynamic characteristics of both pathways were compared on the basis of DFT and ab initio 6-311++G(d,p) quantum chemical calculations.

thiopyrano[4,3- b ]indole-3(5 H )-thiones 和乙炔二甲酸二甲酯 (DMAD)的反应通过两个竞争级联途径进行。最初，这两种途径都从硫代羰基硫和乙炔碳原子相互作用开始。然后发生两个平行过程：炔烃-硫代羰基复分解和 (3 + 2) 环加成。在接下来的阶段，在这两种情况下，噻吩成环和噻喃开环都会进行。最后，中间体硫酮和第二当量 DMAD 的 (4 + 2) 环加成反应导致生成带有噻吩基取代基的噻吩并 [4,3- b ] 吲哚衍生物。基于DFT和从头算6-311++G(d,p) 量子化学计算。