A Domino Cyclization Reaction of Iminium Salts: A Convenient Route to Hexahydrobenzo[b]phenanthrolines

An efficient synthesis of hexahydrobenzo[b]phenan­throlines is described. These compounds are prepared by the reaction of anilines with the prenylated derivatives of 2-, 3- and 4-pyridine carboxaldehydes. This reaction is catalyzed by both 5% TFA and 1% Yb(OTf)3 in MeCN to furnish the targeted products as a 1:1 mixture of diastereomers in a high yields (63-89%).