A Molecular Electron Density Theory Study of the Lewis Acid Catalyzed [3+2] Cycloaddition Reactions of Nitrones with Nucleophilic Ethylenes
Luís R. Domingo, Mar Ríos‐Gutiérrez, Nivedita Acharjee
Abstract
Abstract The BF 3 Lewis acid (LA) catalyzed [3+2] cycloaddition (32CA) reaction of 1‐pyrroline‐1‐oxide (PNO) with 2,3‐dihydrofuran (DHF) has been studied within the molecular electron density theory (MEDT) at the ω B97X‐D/6‐311G(d,p) computational level. Electron localization function (ELF) characterizes PNO and the corresponding PNO : BF 3 complex as zwitterionic species. Conceptual DFT indices allow classifying PNO and DHF as marginal electrophiles and strong nucleophiles, while the PNO : BF 3 complex is a strong electrophile. Consequently, while the non‐catalyzed 32CA reaction is non‐polar, the BF 3 catalyzed one has a high polar character, revealed by the analysis of the global electron density transfer (GEDT) at the transition state structures. The BF 3 catalyzed 32CA reaction, which is classified as of reverse electron density flux (REDF), presents high exo stereoselectivity, and total ortho regioselectivity. The presence of the BF 3 catalyst decreases the activation enthalpy of the 32CA reaction in dichloromethane by 7.5 kcal mol −1 , as a consequence of the increase of the polar character of the reaction, in complete agreement with the experimentally observed acceleration.