In the searching for zwitterionic intermediates on reaction paths of [3 + 2] cycloaddition reactions between 2,2,4,4-tetramethyl-3-thiocyclobutanone S-methylide and polymerizable olefins

Abstract

DFT calculations show that - both in a weakly polar and in a strongly polar medium - the [3 + 2]-cycloaddition of 2,2,4,4-tetramethyl-3-thiocyclobutanone S-methylide with nitroethene takes place according to a polar, two-step mechanism with a zwitterionic intermediate. On the other hand, a similar reaction with less electrophilic t-butyl methacrylate is a single-step process. However, zwitterionic structures with "extended" conformation may be formed in both cases considered here, in a reaction path competitive to cycloaddition.