Investigation of the regio- and stereoselectivity of Diels–Alder reactions by newly developed ABEEM σπ model on the basis of local HSAB principle and maximum hardness principle

On the basis of density functional theory, a scheme for efficient calculating Fukui function, local softness, and hardness within atom-bond electronegativity equalization method plus σπ model is delivered. By the local softness obtained through this model, we investigated the regioselectivity of Diels–Alder reaction in light of local HSAB principle, and the result is in accordance with experimental and theoretical results. Moreover, we demonstrate for the first time that the maximum hardness principle is obeyed in the stereospecific Diels–Alder reactions, i.e., compared with exo isomer, the more stable endo isomer usually has larger hardness value, consequently, composes the main product.