Catalytic alkene cyclization reactions for the stereoselective synthesis of complex "terpenoid-like" heterocycles

A new catalytic synthesis of densely substituted tetrahydroquinolines is described. This reaction forms up to two rings, three bonds, and three stereogenic centers with excellent stereo- and regiocontrol in a single step. Although control experiments demonstrate that the active catalyst is protic acid, Sc(OTf)₃ serves as an effective and practical pre-catalyst. The scope of this reaction is demonstrated with 21 monocyclizations and 14 bicyclization reactions.