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Chiral Phosphanylferrocenecarboxamides with Amino Acid Pendant Groups as Ligands for Cu‐Mediated Asymmetric Conjugate Additions of Diethylzinc to Chalcones – Structural Characterisation of Precursors to the Cu Catalyst
Author(s) -
Tauchman Jiří,
Císařová Ivana,
Štěpnička Petr
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201000480
Subject(s) - diethylzinc , chemistry , ferrocene , chalcone , conjugate , catalysis , ligand (biochemistry) , alkylation , planar chirality , medicinal chemistry , thiourea , stereochemistry , crystal structure , enantioselective synthesis , combinatorial chemistry , organic chemistry , mathematical analysis , biochemistry , receptor , mathematics , electrode , electrochemistry
A series of chiral phosphanylferrocenecarboxamides was prepared by treatment of either 1′‐(diphenylphosphanyl)ferrocene‐1‐carboxylic acid (Hdpf) or its planar‐chiral 1,2‐isomers with amino acid methyl esters in the presence of peptide coupling agents. The compounds were characterised by spectroscopic methods, and the crystal structure of one representative was determined by X‐ray diffraction. Catalytic testing of these donors in Cu‐catalysed asymmetric conjugate additions of diethylzinc to chalcones revealed that the reaction outcomes were highly sensitive to the ligand structure and the reaction conditions (copper source and solvent), whereas the chalcone substituents (Me, MeO, or Cl in positions 4 or 4′) had a less pronounced influence. Compounds based on Hdpf proved to be better ligands than their planar‐chiral analogues. Under optimised conditions, the reactionwith L ‐valine–Hdpf conjugate, ( S )‐Ph 2 PfcCONHCH(CHMe 2 )CO 2 Me (fc = ferrocene‐1,1′‐diyl) and unsubstituted chalcone gave the alkylation product with complete conversion (20 °C/4 h) and in 87 % ee . The catalytic behaviour of the amidophosphane ligands was correlated to the results of amodel coordination study and the crystal structure of [Cu(Ph 2 PfcCONHCH 2 CO 2 Me) 2 ](CF 3 SO 3 ) · 2CHCl 3 .