A theoretical investigation on the regioselectivity of the intramolecular hetero Diels-Alder and 1,3-dipolar cycloaddition reactions of 2-(vinyloxy)benzaldehyde derivatives

The present paper reports a systematic computational analysis study of the two possible pathways, fused and bridged, for an intramolecular hetero Diels-Alder (IMHDA) and an intramolecular 1,3-dipolar cycloaddition (IMDCA) of 2-(vinyloxy)benzaldehyde derivatives. The potential energy surface analyses for both reactions are in agreement with the experimental observations. The activation energies associated with the two regioisomeric channels in the IMHDA reaction showed that the bridged product is favored, although in the IMDCA, the most stable transition state results in the fused product. The global electronic properties of the fragments within each molecule were studied to discuss the reactivity patterns and charge transfer direction in the intramolecular processes. The asynchronicity of the bond formation and aromaticity of the optimized TSs in the Diels Alder reaction as well as cycloaddition reaction were evaluated. Finally, the H-1-NMR chemical shifts of the possible regioisomers were calculated using the GIAO method, the values of which for the most stable products were in agreement with the experimental data for both reactions.