Reductive Nitro-Mannich Route for the Synthesis of 1,2-Diamine Containing Indolines and Tetrahydroquinolines

A one-pot, 1,4-hydride addition nitro-Mannich reaction between a set of nitroalkenes 3 and a wide range of N-p-methoxyphenyl-protected aldimines, derived from alkyl, aryl and heteroaryl aldehydes, followed by Zn/HCl reduction leads to stereochemically defined 1,2-diamines. These underwent palladium-catalyzed cyclization and depending upon the presence or not of the trifluoroacetamide protecting group gave either tetrahydroquinolines 18 or indolines 14 in high overall yield and diastereoselectivity (19 examples each). In each case, the more nucleophilic pendant amine cyclizes to give a benzofused saturated heterocyclic 5- or 6-membered ring, with an additional vicinal amino stereocenter in each.