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 beta-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 beta-elimination are observed.