Revisiting the Hirao cross-coupling: improved synthesis of aryl and heteroaryl phosphonates
摘要:
The palladium-catalyzed cross-coupling of dialkylphosphite with aromatic electrophiles (Hirao coupling) was re-investigated. Some limitations in terms of palladium loadings and substrate reactivity are alleviated with the use of Pd(OAc)(2) complexed to 1,1'-bis(diphenylphosphino) ferrocene (dppf) as a ligand. Various aryl and heteroaryl halides are employed to deliver both known and novel substituted phosphonates. The first examples of aryl chloride couplings are also reported. (C) 2008 Elsevier B.V. All rights reserved.
Four new bidentate phosphine ligands have been synthesized, characterized and evaluated in Ni-catalyzed C-P coupling reaction. The readily available and inexpensive highly active sulfonate Ni(cod)(2)-L8catalyzes the reaction leading to the desired aryl phosphonates accumulated with moderate to excellent yields. This method is characterized by good functional groups tolerance, wide substrate scope, and easy scaling up.