Nucleophilic Addition of Ketones To Acetylenes and Allenes: A Quantum-Chemical Insight

Abstract

A CBS-Q//B3 based study has been carried out to elucidate the mechanism of the KOH/DMSO superbase catalyzed ketones nucleophilic addition to alkyl propargyl and alkyl allenyl ethers yielding, along with (Z)-monoadducts, up to 26% of unexpected (E)-diadducts. The impact of different substrates (alkynes versus allenes) on the reaction mechanism has been discussed in detail. Along with the model reaction of acetone addition to propyne and allene, the addition of acetone and acetophenone to methyl propargyl and methyl allenyl ethers is considered. The limiting reaction stage of the starting ketone carbanion addition to propargyl and allenyl systems occurs with activation energies typical for vinylation of ketones. In contrast, the addition of intermediate α-carbanions to the terminal position of methyl allenyl ether is associated with unusually low activation barriers. The results obtained explain the composition of the reaction products and indicate the participation of mainly the allene form in the reaction.

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

“…For the same reason, it turns out that the optimization of geometry of investigated systems with the MP2 method (as well as using the double‐hybrid functionals such as B2PLYP) is resource‐intensive for serial calculations. Simpler functionals, particularly the popular B3LYP, provide sufficient efficiency and reliable geometries of stationary points but can lead to significant errors in activation barriers and relative stability of isomeric forms of alkynes involved in reactions . This led us to investigate the applicability of other approaches, particularly composite approaches, for describing the cascade reactions of acetylene, which are based on the optimization of geometrical parameters and calculation of vibrational corrections at the level of B3LYP/6‐31+G* (such as in the accurate CBS‐Q//B3 approach in combination with a slightly different basis set) and refining the stationary point energy with a single‐point calculation using more accurate methods.…”

“…To estimate the activation free energy in solution, we used an approach that is based on the results of Wertz proposed in Ref . Being applied to dimethyl sulfoxide solutions, this approach suggests that the entropy in the DMSO solution S sol can be obtained from the entropy for ideal gas in the harmonic approximation ( S harm ) as follows: …”

“…In such systems, cations are most often represented by an alkali metal (M = Li, Na, K, Rb, Cs) or tetraalkylammonium cations, while hydroxide, alkoxide, amide, hydrosulfide, alkyl sulfide ions and carbanions act as anions. Studies of physical organic properties and the reactivity of KOH/DMSO mixtures demonstrated an extraordinary basicity (pK a [30][31][32] that was suggested to result from a synergism of two bases according to the definition of superbase by Caubere. [20] It is assumed that the specific solvation of the cation, and hence the increased activity of the base anion, is the reason of the superbasicity of such systems.…”

Two classes of heterocycles—6,8‐dioxabicyclo[3.2.1]octanes and cyclopentenols from the same reagents: A quantum‐chemical comparison of mechanism

“…Here, we extended this approach to dimethyl sulfoxide solutions. A consistent application of the Wertz method allows one to estimate the entropy in a DMSO solution as where S harm means the entropy found in the harmonic approximation for ideal gas.…”

How does HOTf/HFIP Cooperative System Catalyze the Ring‐Opening Reaction of Cyclopropanes? A DFT Study

“…[6] Considering the default standard state in the Gaussian 09 program is gas phase (1 atm), corrections should be made for Gibbs freeenergy determinations in solution. [14] As the concentration of the reactant is 2 M, corrections of À 2.2 or 2.2 kcal/mol were made for reaction steps involving two species to one species or one species to two species in Gibbs free-energy determinations. Similarly, corrections of À 0.8 or 0.8 kcal/mol were made for reaction steps involving addition or removal of a molecule of HOTf (see Supporting Information for details).…”