Rapid synthesis of tetrahydroquinolines by indium trichloride catalyzed mono- and bis-intramolecular imino Diels-Alder reactions

A rapid synthesis of mono- and bis-tetrahydropyrazolo[4′,3′:5,6]thiopyrano[4,3-b]quinolines has been achieved by the reaction of aldimines derived from aromatic amines and S-prenylated aldehydes in acetonitrile with InCl3 as a catalyst, in excellent yields and short reaction times, under mild conditions.