Theoretical Investigations on [3,3] Sigma tropic Rearrangements in 1‐Formyl‐2‐Vinyl Cyclobutane/Lactam

Abstract The current manuscript discusses the density functional based ab initio investigations of [3,3] oxa‐Claisen rearrangement reactions involving functionalized 1‐formyl‐2‐vinyl cyclobutane/lactam, emphasizing their expected transformations into various 8 membered heterocycles. The most feasible molecular assembly for the targeted [3,3] oxa‐Claisen rearrangement of functionalized 1‐formyl‐2‐vinyl cyclobutane/lactam has been identified. Reaction parameters, including reaction and activation energies, have been calculated and compared. The theoretical effect of various substituents (H, Ph, SO 2 Ph) at different positions of the tethered 4‐vinyl and 3‐oxa functionalities of cyclobutane/lactams has also been studied for the proposed [3,3] carba‐Claisen rearrangement of 1‐formyl‐2‐vinyl cyclobutane/lactam. Our findings suggest an energy barrier ranging from 50 to 100 kcal/mol for most rearrangements. We observed a reduction in the energy barrier of 20 to 52 kcal/mol with a polar solvent, whereas a decrease of 8 to 30 kcal/mol was noted with a nonpolar solvent. The [3,3] Claisen rearrangement of the functionalized 2‐vinyl cyclobutane/lactam carba‐aldehydes demonstrates an exothermic reaction.