Synthesis of tetrahydroquinoline derivatives with triflate catalyzed aza Diels-Alder reactions

The heterocyclic systems and their substituted derivatives that have an important place in organic chemistry are widely used in industry and medicine. The Diels-Alder reactions of imines allow an easy access to nitrogen-containing six-membered heterocyles, such as pyridines and quinolines. Kobayashi and co-workers have reported rare earth triflates are quite effective for the catalytic activation of imines. The triflates work as Lewis acids; they are stable in water, can be recovered after reactions are completed and can be reused and only a catalytic amount of the triflate is enough to complete the reactions.We examined the Diels-Alder reactions of imin compounds which were obtained from substituted arylaldehydes and p-toluidine, with cyclopentadien in the presence of a catalytic amount of rare metal trifate such as Yb(OTf)3. The effects of metal triflates have been investigated in several reactions. Some new tetrahydroquinoline derivatives were obtained in high yields.The structures of the obtained new compounds have been clarified by spectroscopic methods after the purification processes.