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Updated: May 6, 2026

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
Mechanistic Insights into the Base-Mediated (3 + 2) Cycloaddition of N-Benzyl Ketimines to Acetylenes: A DFT Study
Anastasiya G Pradedova1, Vladimir B Kobychev1
1Laboratory of Quantum Chemical Modeling of Molecular Systems, Irkutsk State University, 1 K. Marks Street, 664003 Irkutsk, Russian Federation.
Abstract:
In the context of density functional theory, the B2PLYP-D3/6-311+G**//B3LYP-D3/6-31+G* combined approach was utilized to investigate the mechanism of (3 + 2) cycloaddition of N-benzyl-1-phenylethan-1-imine to phenylacetylene yielding 2-methyl-2,3,5-triphenyl-1-pyrroline. Three distinct pathways have been identified, each contributing differently depending on the changing ratios of reactants during the course of the reaction. Possible pathways for the formation of the major (2R,3R)- and minor (2R,3S)-diastereomers are considered, as well as the oxidation of 2-methyl-2,3,5-triphenyl-1-pyrroline with chloranil to 2-methyl-2,3,5-triphenyl-2H-pyrrole.
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Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism

