The stereoselective synthesis of ( Z)-HFC [dbnd]CFZnI and stereospecific preparation of ( E)-1,2-difluorostyrenes from ( Z)-HFC [dbnd]CFZnI via an unusual Pd(PPh 3) 4–Cu(I)Br co-catalysis approach or ( Z)-HFC [dbnd]CFSnBu 3

Abstract

( Z)-HFC CFZnI was stereoselectively synthesized from activated zinc dust and ( Z)-HFC CFI that was synthesized from chlorotrifluoroethene in a sequential manner. Compared to ( E)-HFC CFZnI, ( Z)-HFC CFZnI was more challenging to prepare in terms of sluggish metallation and formation of by-products, and underwent slower and incomplete Negishi coupling with aryl iodides. In a modification of Negishi coupling, ( E)-α,β-difluorostyrenes were stereospecifically prepared in good to excellent yields under mild conditions from aryl iodides and ( Z)-HFC CFZnI with the co-catalysis of Pd(PPh 3) 4/Cu(I)Br. Experimental investigation and mechanistic rationalization suggested that Cu(I)Br would be a scavenger of free ligands for the facilitation of Pd(PPh 3) 2 formation, and a supplier of ligand for the metathesis process. Alternatively, ( Z)-HFC CFSnBu 3 and aryl iodides with an electron-withdrawing group underwent Stille–Liebiskind coupling to afford ( E)-α,β-difluorostyrenes.