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

Abstract

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.

Aldol Condensation Versus Superbase-Catalyzed Addition of Ketones to Acetylenes: A Quantum-Chemical and Experimental Study

“…Thus, under the interaction of acetone with acetylene, the reactions of aldol condensation and ethynylation, as well as further transformations with the participation of the products of these reactions predominate. However, to initiate cascade assemblies leading to the formation of 6,8-dioxabicyclo[3.2.1]­octanes and acylcyclopentenols, it is required that at the first stage, acetone interacts with acetylene in the direction of nucleophilic addition to the triple CC bond of acetylene ( C -vinylation reaction). , …”

“…These are (i) the acetone C -vinylation reactions, (ii) the reaction of acetone aldol condensation into isophorone, and finally (iii) the ethynylation reactions followed by alcohol autovinylation. Note that the mechanisms of the reactions of ethynylation and C -vinylation of acetone with unsubstituted acetylene were studied in detail in our earlier works, , and in the present work, they were only recalculated within the adopted B2PLYP­(D2)/6-311+G**//B3LYP/6-31+G* approach. Additionally, in this work, the forward and reverse activation barriers for autovinylation of methyl-3-butyn-2-ol were calculated.…”

“…The B2PLYP functional, which provides “chemical” accuracy in various tests, − was not among the functionals studied in ref . In our recent studies, the B2PLYP/6-311+G**//B3LYP/6-31+G* approach has been successfully used to describe various reactions of ketones with acetylenes carried out in superbasic media, including the steps of vinylation and ethynylation, isomerization of the multiple bond position, reactions of nucleophilic addition to a double bond, in which unsaturated ketones act as the Michael acceptors, and so forth . For the aldol reaction of acetone in the gas phase, this approach with the inclusion of the D2 Grimme dispersion correction gives the estimate Δ H = −8.2 kcal/mol, which is in good agreement with the data of the reference calculation CBS-QB3 (Δ H = −9.2 kcal/mol).…”

“…However, to initiate cascade assemblies leading to the formation of 6,8-dioxabicyclo[3.2.1]octanes and acylcyclopentenols, it is required that at the first stage, acetone interacts with acetylene in the direction of nucleophilic addition to the triple CC bond of acetylene (C-vinylation reaction). 11,38 To understand the reasons of this atypical behavior of acetone in the superbase-promoted reactions with acetylene, it is reasonable to compare the kinetic characteristics of all three competing reactions that can occur in the acetone/ unsubstituted acetylene system. These are (i) the acetone Cvinylation reactions, (ii) the reaction of acetone aldol condensation into isophorone, and finally (iii) the ethynylation reactions followed by alcohol autovinylation.…”

Understanding the solubilization of Ca acetylide with a new computational model for ionic pairs

“…52 Acetylene chemistry in dimethyl sulfoxide (DMSO) under basic and super-basic conditions is a valuable and indispensable tool of modern organic chemistry. 46,[53][54][55][56] Greater potential of practically valuable synthesis with CaC 2 can be realized through understanding the unique performance of DMSO solutions.…”