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.