Pd(II)-Catalyzed Aerobic Intermolecular 1,2-Diamination of Conjugated Dienes: A Regio- and Chemoselective [4 + 2] Annulation for the Synthesis of Tetrahydro­quinoxalines

A Pd­(II)-catalyzed
aerobic intermolecular 1,2-diamination of conjugated
dienes was developed for the regio- and chemoselective preparation
of a variety of functionalized tetrahydro­quinoxalines, using
simple sulfonyl protected o-phenylendiamines as a
nitrogen source. This methodology provides a direct and efficient
synthesis of tetrahydro­quinoxalines. O2 was used
as the stoichiometric oxidant, and reaction conditions were applied
to a series of o-phenylendiamines and conjugated
dienes. 35 examples are described, and good yields and selectivities
are obtained for the majority of the products.