Nitrogen Assistance in Intramolecular Nickel-Promoted Tandem Cyclization−Quenching Processes

A diastereoselective and mild cyclization−quenching process based on the treatment of nitrogen-tethered halodienes with stoichiometric Ni(COD) 2 is described. The success of this methodology relies on the presence of a distal amino group capable of coordinating with the metal in the transient vinyl or alkylnickel species, thus controlling the diastereoselectivity of the cyclization step and preventing Ni−H β-elimination prior to the quenching. In general, better results are obtained in cyclizations taking place via a 5-exo-trig process, and a diversity of mono- and bicyclic nitrogenated systems are afforded in high yields by the proper choice of starting halodienes and quenching reagents. The presence of 2,2‘-bipyridine as a ligand results in an acceleration of the process, and in some cases, higher diastereoselectivities and/or supression of the Ni−H β-elimination are observed.