An investigation of the regio-, chemo-, and stereoselectivity of cycloaddition reactions of 2-phenylsulfonyl-1,3-butadiene and its 3-phenylsulfanyl derivative: a DFT study

Abstract

The cycloaddition reactions of 2-sulfonyl dienes with some alkenes have been investigated using density functional theory (DFT)-based reactivity indices and activation energy calculations at the MPWB1K/cc-pVDZ level of theory. Two modes of [4+2] and [2+4] cycloaddition reactions can occur from the results of cross-Diels-Alder reactions of 2-sulfonyl dienes, with 2,3-dimethyl butadiene and or cyclopentadiene. The energy results indicated that the [2+4] cycloaddition reactions are the most favorable pathways. The considerable difference in the electron deficiency can lead to the different reactivity of the two C-C double bonds of the 2-sulfonyl diene. Moreover, the phenylsulfanyl group is a much more powerful directing element than the phenylsulfonyl group (SO2Ph) for the control of the regioselectivity of cycloaddition reactions. The reactions take place via an asynchronous one-step mechanism with a polar character, and an analysis of the conceptual DFT indices explains the polar character of these reactions. The electron reorganization along the most preferred pathway of the [2+4] cycloaddition reaction between 2-phenylsulfonyl-1,3-butadienes and cyclopentadiene have been studied using the topological analysis of the electron localization function (ELF). The ELF analysis revealed that this reaction proceeds through a two-stage one-step mechanism.