Aminopyrimidines as electron-rich azadienes: Extension of the synthetic potential of hetero Diels-Alder reactions under acidic conditions

By addition of a catalytic amount of a strong acid and selection of the app ropriate solvent, the cycloaddition reactions of dimethyl acetylenedicarbox ylate (DMAD) to 6-aminopyrimidine derivatives drastically changed their cou rse leading to new products, pyrrolo[3,4-c]pyridines, which were different from those obtained in the absence of acid. This change was interpreted on the basis of acid interception of the non-isolable adducts formed by initia l hetero Diels-Alder cycloaddition between the reactants.