The mechanisms of fundamental base‐promoted acetylene reactions, namely, nucleophilic addition to the triple C ≡ C bond (vinylation) and nucleophilic addition of acetylenic carbanion to a carbonyl group (ethynylation), are addressed using three models of different complexity—pentasolvate, monosolvate, and anionic—which describe the catalytic superbasic systems MOH(OBut)/DMSO (suspensions of alkali hydroxides or tert‐butoxides in dimethyl sulfoxide). The above acetylene reactions and sequential transformations of reagents arranged by the superbasic center are modeled within the framework of the most complete pentasolvate model, in which the superbase is represented by the KOH·5DMSO (KOBut·5DMSO) complexes. We have developed approaches to the construction of simplified models (monosolvate and anionic) to describe transformations in complex systems. The mechanisms of cascade assemblies of 6,8‐dioxabicyclo[3.2.1]octanes, cyclopentenones, and furan cycles from ketones and acetylenes in the superbasic environment are investigated using a uniform B2PLYP/6‐311+G**//B3LYP/6‐31+G* approach, and the energy profiles of these different carbo‐ and heterocycles are analyzed.

By employing the contemporary B2PLYP­(D3)/6-311+G**//B3LYP/6-31+G* method of quantum chemistry, we unraveled the mechanism of a recently discovered cascade assembly of N-phenyl-2,5-dimethylpyrrole from one molecule of aniline and three molecules of acetylene activated by KOH/DMSO and KOBu t /DMSO superbase systems. For the established mechanism, we compare and analyze the activity of these two superbases. The reaction is found to be activated by the interaction of aniline with acetylene, and the barrier associated with this interaction turns out to be the limiting one. Another barrier close in value to the limiting one is found along the cascade assembly pathway and relates to ethynylation of N-but-3-yn-2-yl-aniline by the ethynide ion. The cascade reaction turns out to be selective with respect to propyne–allene rearrangements. The alternative mechanism of N-phenyl-2,5-dimethylpyrrole self-assembly, which involves a preliminary stage of acetylene oligomerization, is shown to be kinetically less favorable.

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