Cyclizations of phenylethyl-substituted pyridinecarboxaldehydes.

Several phenylethyl-substituted pyridinecarboxaldehydes were prepared from 2-bromo-3-pyridinecarboxaldehyde and these substances are found to undergo cyclization reactions in acidic media. In the absence of added nucleophile, acid promoted cyclization and oxidation (MnO2) provides 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.