Enantioselective Allylic Substitution Catalyzed by Chiral [Bis(dihydrooxazole)]palladium Complexes: Catalyst structure and possible mechanism of enantioselection

DOI Web Site Web Site 被引用文献7件

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公開日
1995-03-22
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1002/hlca.19950780202
公開者
Wiley

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<jats:title>Abstract</jats:title><jats:p>Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of <jats:italic>rac</jats:italic>‐1,3‐diphenylprop‐2‐enyl acetate (<jats:italic>rac</jats:italic>‐<jats:bold>5</jats:bold>) with the anion of dimethyl malonate (<jats:italic>Scheme 1</jats:italic>). Using enantiomerically pure (<jats:italic>S</jats:italic>,<jats:italic>E</jats:italic>)‐1‐(4‐tolyl)‐3‐phenylprop‐2‐enyl acatete ((<jats:italic>S</jats:italic>)‐<jats:bold>25</jats:bold>) as substrate, the reaction was shown to proceed by a clean ‘<jats:italic>syn</jats:italic>’ displacement of acetate by dimethyl malonate (<jats:italic>Scheme 6</jats:italic>). The [Pd<jats:sup>11</jats:sup>(η<jats:sup>3</jats:sup>‐allyl)] complex <jats:bold>18</jats:bold> and the analogous [Pd(η<jats:sup>3</jats:sup>‐1,3‐diphenylallyl)] complex <jats:bold>20</jats:bold>, 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 PdC bond and a shift of the corresponding <jats:sup>13</jats:sup>C‐NMR resonance to higher frequency.</jats:p>

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