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The stereoselective synthesis of (Z)-HFCCFZnI and stereospecific preparation of (E)-1,2-difluorostyrenes from (Z)-HFCCFZnI via an unusual Pd(PPh3)4-Cu(I)Br co-catalysis approach or (Z)-HFCCFSnBu3
Authors:Qibo Liu
Institution:Department of Chemistry, The University of Iowa, Iowa City, IA 52242, United States
Abstract:(Z)-HFCdouble bond; length as m-dashCFZnI was stereoselectively synthesized from activated zinc dust and (Z)-HFCdouble bond; length as m-dashCFI that was synthesized from chlorotrifluoroethene in a sequential manner. Compared to (E)-HFCdouble bond; length as m-dashCFZnI, (Z)-HFCdouble bond; length as m-dashCFZnI 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)-HFCdouble bond; length as m-dashCFZnI with the co-catalysis of Pd(PPh3)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(PPh3)2 formation, and a supplier of ligand for the metathesis process. Alternatively, (Z)-HFCdouble bond; length as m-dashCFSnBu3 and aryl iodides with an electron-withdrawing group underwent Stille-Liebiskind coupling to afford (E)-α,β-difluorostyrenes.
Keywords:Cuprous bromide  Cuprous complex  Palladium catalysis  (Z)-1  2-Difluoroethenyl zinc iodide  (Z)-1  2-Difluoroethenyltributylstannane  Zinc iodide  (E)-1  2-Difluorostyrenes
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