Diels–Alder Reactions of a Thiazole o-Quinodimethane with 2- and 3-Bromo-5-hydroxynaphthoquinones. A Theoretical Study

PM3, molecular hardness and ab initio (3-21G∗) calculations were performed in order to explain the high regioselectivities observed in the Diels–Alder reactions of o-QDM 2 and 2- or 3-bromo-5-hydroxynaphthoquinones 3a and 4a. The theoretical findings of this study agree with the experimental results and support the statement that hydrogen bonding plays a crucial role on the regiocontrol of the cycloadditions.