Theoretical study of the regio- and stereoselectivity of the 1,3-DC reaction of 2,3,4,5-tetrahydropyridine-l-oxide with methyl crotonate

A theoretical study of the regio- and stereoselectivities of the 1,3-dipolar cycloaddition reaction between methyl crotonate and 2,3,4,5-tetrahydropyridine-l-oxide has been carried out using density functional theory (DFT) calculations at B3LYP/6-31G(d) level of theory. Analysis of the global reactivity and local electrophilicity indices has been used to explaining the regioselectivity of the titled reaction. Overall, our results show that the studied 1, 3-dipolar cycloaddition reactions favor the formation of the meta-endo cycloadduct in both cases. The bond order and charge transfer at the transition states and activation energies indicate that these reactions proceed via an asynchronous concerted mechanism. Thermodynamic and kinetic quantities for the possible stereoisomeric and regioisomeric pathways have been calculated at gas and solvent phase. Solvent effects do not modify the gas-phase selectivities but slightly increases the reactivity of the reagents. A good concordance is found between the obtained results and the experimental outcomes.