Comparative DFT study on the platinum catalyzed [3 + 2] and [2 + 2] cycloaddition reactions between the derivatives of allene and alkene

Abstract

A comparative study on [3 + 2] and [2 + 2] cycloaddition processes between alkene and allene derivatives, under the catalytic action of platinum salt, has been performed using DFT quantum mechanical method. Our study reveals that the metal bound allenes react through a stepwise pathway with alkene system leading to a tetracyclic or pentacyclic products. The unsubstituted reactants reveal only the [3 + 2] reaction by crossing a high activation barrier to generate cyclopentane derivative. Presence of oxygenated substituents on the reactants raises the possibility of both [2 + 2] and [3 + 2] cycloaddition processes. Variation of substituents to control the bulkiness may tune the reaction to progress selectively in a specific direction leading to a specific ring sized product in high yield. The study also explains the experimentally observed selectivity for the metal catalysed cyclization in generating tetra or pentacyclic structure.