Understanding the mechanism of [3 + 2] cycloaddition reaction of benzoisothiazole-2,2-dioxide-3-ylidene with nitrones

Abstract

A theoretical investigation was carried out on the mechanism and regioselectivity of the [3 + 2] cycloaddition (32CA) reaction of benzoisothiazole-2,2-dioxide-3-ylidene with nitrone using Molecular Electron Density Theory through DFT calculations at B3LYP and wB97xD functionals with 6-31G(d,p) basis set in the gas phase and toluene. Hard and soft acids and bases principle, Parr functions, as well as potential energy surface analysis were utilized for studying the regio- and stereoselectivity of this reaction, and the obtained results are consistent with the experimental observations. The electron localization function analysis of the nitrone shows that there is a double bond between N and C in the absence of any carbenoid or pseudoradical center. Therefore, a zwitterionic structure for nitrone 2 can be suggested, expected that its 32CA reaction is zw-type. The noncovalent interactions topological analysis shows that the first sigma bond has been formed before reaching the TS, which is in line with a two-stage one-step mechanism.