Bismuth(III) chloride-catalyzed intramolecular hetero-Diels–Alder reactions: a novel synthesis of hexahydrodibenzo[b,h][1,6]naphthyridines

BiCl3 efficiently catalyzed the intramolecular hetero-Diels–Alder reactions of aldimines generated in situ from aromatic amines and the N-allyl derivative of o-aminobenzaldehyde in refluxing acetonitrile to afford a novel class of hexahydrodibenzo[b,h][1,6]naphthyridine derivatives. The products are isolated as mixtures of trans and cis diastereoisomers in a 1:1 ratio, in good to excellent yields.