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Stereoselective Carbonyl Allylation by Umpolung of Allylpalladium(II) Complexes
Author(s) -
Zai Giuseppe,
Pontiroli Alessandro,
Marchetti Alberto,
Vidari Giovanni
Publication year - 2007
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.200700054
Subject(s) - umpolung , chemistry , nucleophile , transmetalation , stereoselectivity , aldehyde , palladium , reactivity (psychology) , allylic rearrangement , moiety , medicinal chemistry , reagent , stereochemistry , organic chemistry , catalysis , medicine , alternative medicine , pathology
The nucleophilic palladium‐mediated allylation of a carbonyl group requires the inversion of the reactivity (umpolung) of the η 3 ‐allylpalladium moiety. If the reaction is performed with a metal more electropositive than palladium, the stereochemical outcome is influenced by the solvent and by the reagent used for the umpolung. The stereoselectivity is also determined by the rate of η 3 –η 1 –η 3 equilibration of the η 3 ‐allylpalladium system relative to that of the transmetallation and addition to the aldehyde. When the umpolung is carried out with η 1 ‐ or bis(allylpalladium) complexes, the stereoselectivity mainly depends on the nature of the substituents on the allyl fragment. Asymmetric addition has been achieved by using chiral ligands that promote palladium‐mediated reactions with “hard” nucleophiles. Utilization of selected chiral monophosphanes/phosphoramidite as ligands induces enantioselectivity that depends on the nature of the aldehyde as well as of the umpolung agent. Modest enantiomeric excesses have been obtained by using preformed bis(allylpalladium) systems with one chiral allylic fragment.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)