Highly Efficient Ligands for the Palladium-Assisted Double N-Arylation of Primary Amines for One-Sep Construction of Carbazoles

A highly efficient one-pot synthesis of carbazoles via palladium-catalyzed double N-arylation of primary amines with 2,2'-dihalobiphenyls is described using a catalyst system comprised of tris(dibenzylideneacetone)dipalladium(0) (Pd(2)dba(3)) and the proazaphosphatrane P(i-BuNCH2CH2)(3)N (8) or its derivative (t-Bu)(2)P=N-P(i-BuNCH2CH2)(3)N (9a) as the ligand. The process is effective for double N-arylation of 2,2'-biphenyl dibromide, diiodide, and even dichloride with a variety of primary amines including neutral, electron-rich, electron-deficient, and sterically hindered anilines as well as aliphatic amines.