Role of hydroxyl groups on the aromatic ring in the reactivity and selectivity of the reaction of β-phenylethylamines with non-enolizable aldehydes

The influence of hydroxyl groups on the beta-phenylethylamine aromatic ring was studied during its reaction with non-enolizable aldehydes. Computational calculations established that the degree of hydroxylation generates differences in the activation patterns of the ring (different reaction pathways) and in the nucleophilicity of the nitrogen atoms (different reaction yields). Cyclic aminals, benzoxazinephanes, or tetrahydroisoquinolines were obtained in the reaction with formaldehyde, and Schiff's bases or tetrahydroisoquinolines were produced in the reaction with other non-enolizable aldehydes. The product obtained depends on the degree of hydroxylation of the ring of the starting phenylethylamine.