Synthesis of Tetrahydroquinolines via a Vinylogous Aza-Povarov Reaction

Significance

Reported is the first example of a vinylogous aza-Povarov reaction (L. S. Povarov Russ. Chem. Rev. 1967, 36, 656-670) of aromatic imines and N-amino-1-azadienes under indium catalysis yielding 1,2,3,4-tetrahydroquinolines in good to excellent yields with complete diastereoselectivity. The products, bearing C-4 heteroatom containing short-chain substituents are reminiscent of biologically relevant tetrahydroquinolines. This method uses readily available starting materials and a non-toxic inexpensive catalyst. A rationale for the diastereoselectivity was proposed and NOESY was used to confirm the cis-C-2-C-4 relationship. Complete stereochemical control in the generation of the C-4 quaternary stereocenter is particularly noteworthy.