Cyclizations of phenylethyl-substituted pyridinecarboxaldehydes

Several phenylethyl-substituted pyridinecarboxaldehydes were prepared from 2-bromo-3-pyridine-carboxaldehyde and these substances are found to undergo cyclization reactions in acidic media. In the absence of added nucleophile, acid-promoted cyclization and oxidation (MnO2) provide an efficient route to 10,11-dihydro-5H-benzo[4,5]cyclohepta[1,2-b]pyridin-5-ones. Arene nucleophiles may also be added to the acidic mixture to provide good yields of triarylmethane products. Mechanisms are proposed involving dicationic superelectrophilic intermediates.