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Enantioselective Allylic Substitution Catalyzed by Chiral [Bis(dihydrooxazole)]palladium Complexes: Catalyst structure and possible mechanism of enantioselection
Author(s) -
Matt Peter Von,
LloydJones Guy C.,
Minidis Alexander B. E.,
Pfaltz Andreas,
Macko Ludwig,
Neuburger Markus,
Zehnder Margareta,
Rüegger Heinz,
Pregosin Paul S.
Publication year - 1995
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19950780202
Subject(s) - chemistry , allylic rearrangement , enantioselective synthesis , dimethyl malonate , malonate , ligand (biochemistry) , steric effects , medicinal chemistry , palladium , stereochemistry , substitution reaction , reactivity (psychology) , nucleophile , catalysis , nucleophilic substitution , organic chemistry , medicine , biochemistry , receptor , alternative medicine , pathology
Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac ‐1,3‐diphenylprop‐2‐enyl acetate ( rac ‐ 5 ) with the anion of dimethyl malonate ( Scheme 1 ). Using enantiomerically pure ( S , E )‐1‐(4‐tolyl)‐3‐phenylprop‐2‐enyl acatete (( S )‐ 25 ) as substrate, the reaction was shown to proceed by a clean ‘ syn ’ displacement of acetate by dimethyl malonate ( Scheme 6 ). The [Pd 11 (η 3 ‐allyl)] complex 18 and the analogous [Pd(η 3 ‐1,3‐diphenylallyl)] complex 20 , both containing the same bis(dihydrooxazole) ligand, were characterized by X‐ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer PdC bond and a shift of the corresponding 13 C‐NMR resonance to higher frequency.