Quantum‐chemical models of KOH(KOBut)/DMSO superbasic systems and mechanisms of base‐promoted acetylene reactions

The mechanisms of fundamental base-promoted acetylene reactions, namely, nucleophilic addition to the triple C equivalent to 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 center dot 5DMSO (KOBut center dot 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.