Insights into the mechanism and regiochemistry of the 1,3-dipolar cycloaddition reaction between benzaldehyde and diazomethane

Abstract

The 1,3-dipolar cycloaddition reaction of benzaldehyde with diazomethane is investigated, in gas phase and in diverse polar solvents, using the molecular electron density theory through density functional theory calculations at the B3LYP(+D3)/6-31G(d) level. Analysis of the reaction pathway reveals that this reaction takes place along a concerted but asynchronous mechanism. Computations show that the acetophenone product is kinetically and thermodynamically more favored than 2-phenylacetaldehyde product in agreement with experimental outcomes. The favored cyclization mode and the observed regioselectivity of this cycloaddition are rationalized by both activation energy calculations, frontier molecular orbital analysis and reactivity indices. Also, polar solvents effect favors the reaction. Furthermore, we performed electron localization function (ELF) topological analysis. The ELF topological analysis of diazomethane indicates that this reactant presents an allenic pseudoradical electronic structure.