The molecular mechanism and stereoselectivity of the BF 3 Lewis acid catalyzed [3+2] cycloaddition (32CA) reaction between C-methoxycarbonyl nitrone and cyclopentene have been theoretically studied using DFT methods at the MPWB1K/6-31G(d) computational level. The BF 3 catalyst accelerates the 32CA reaction by decreasing the activation energy leading to the formation of the trans cycloadduct as the kinetic product, in agreement with the experimental data. Inclusion of solvent effects slightly increases the activation energy and decreases the exothermic character of the 32CA reaction as a consequence of a better solvation of nitrone than the transition state and the cycloadduct.The use of the lithium cation as LA catalyst does not make any remarkable change with respect to the BF 3 catalyzed process. The nature of the mechanism has been also studied using the reactivity indices defined within the conceptual DFT.

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The 1,3‐dipolar cycloaddition (13DC) reactions of nitrile‐oxide NO 1 with two ethylenes, enamine 2a and enamine 2b, were computationally studied using B3LYP/6‐31G(d) DFT methods. The two possible ortho and meta regioselective channels were characterized and analyzed. The moderate polarity of these 13DC reactions is related to the high nucleophilic character of both ethylenes, and the moderate electrophilic nature of the NO 1, that accounts for the relatively low calculated activation energies. Analysis of different forms of energies along the different reaction channels indicates that the present 13DC reactions are completely ortho regioselective, accordingly to the experimental outcomes. Electron localization function analysis indicates that these 13DC reactions proceed via a nonconcerted (two‐stage) one‐step mechanism.