Lewis acid mediated domino reaction between 2-cyclohexenone and methyl azide - A DFT study

Abstract

We have studied the Lewis acid mediated domino reaction between 2-cyclohexenone and methyl azide at the B3LYP/6-31G* and B3LYP/6-31+G**//B3LYP/6-31G* levels of theory. A complete survey of the potential energy surface is presented, and the structures of the stationary points and the corresponding molecular mechanism are discussed. The calculations suggest that the product, a cyclopentanone derivative, is formed by means of a domino process that comprises three consecutive reactions. The first and rate-limiting step is a concerted 1,3-dipolar cycloaddition between the Lewis acid coordinated cyclohexenone and methyl azide that yields the corresponding bicyclic 1,2,3-triazoline. The second reaction is a concerted process that includes the extrusion of nitrogen followed by a concomitant skeletal rearrangement to yield the corresponding cyclopentanone derivative. Finally, this cyclopentanone equilibrates to the thermodynamically more stable exocyclic cyclopentanone by means of a stepwise tautomerization of the corresponding iminone. Solvent effects (dichloromethane) were taken into account by using a polarizable continuum model. The results show that no significant changes in the energy profile were found. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.