A Novel Palladium-Catalyzed Synthesis of 1,2-Dihydroquinoxalines and 3,4-Dihydroquinoxalinones

Reactions of enamines, derived from 2-nitroanilines and alpha-substituted aldehydes, with carbon monoxide (6 atm) in the presence of a catalytic amount of bis(dibenzylideneacetone)palladium(0) (Pd(dba)(2)) and 1,3-bis(diphenylphosphino)propane (dppp) afford readily separated mixtures of 1,2-dihydroquinoxalines and 3,4-dihydroquinoxalinones. Addition of a catalytic amount of 1,10-phenanthroline to the reaction mixture substantially improved the yield of products. [reaction: see text]