Density functional theory study of the regio- and stereoselectivity of diels-alder reactions of 5-Aryl-2-pyrones

A theoretical study of the mechanism and regio- and stereoselectivity of DielsAlder reactions of 5-aryl-2-pyrones (Ar = Ph, 4-(MeS)-Ph) with substituted alkenes (CHZ = CH2, Z = COMe, OAc) is performed at the B3LYP/6-31G(d) level. The analysis of the relevant stationary points of the potential energy surface and intrinsic reaction coordinate calculations show that these cycloadditions are undergoing through asynchronous concerted mechanisms yielding to the formation of the 5-endo isomers as the major cycloadducts. The calculation of activation and reaction energies indicates that the 5-endo cycloadducts are favored both kinetically and thermodynamically. The obtained results are in good agreement with experimental outcomes. (c) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011