Mechanistic Insights into the Base-Mediated (3 + 2) Cycloaddition of N -Benzyl Ketimines to Acetylenes: A DFT Study

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 (2 R,3 R )- and minor (2 R,3 S )-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-2 H -pyrrole.