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Influences on the Regioselectivity of Palladium‐Catalyzed Allylic Alkylations
Author(s) -
Kazmaier Uli,
Stolz Daniel,
Krämer Katja,
Zumpe Franz L.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701332
Subject(s) - regioselectivity , allylic rearrangement , isomerization , palladium , chemistry , nucleophile , aryl , catalysis , alkyl , tsuji–trost reaction , medicinal chemistry , organic chemistry
Chelated amino acid ester enolates are excellent nucleophiles for palladium‐catalyzed allylic alkylations. These enolates react rapidly at −78 °C and in general without isomerization of π‐allyl palladium complexes. Therefore, they are good candidates for mechanistic studies and regioselective reactions. Terminal π‐allyl palladium complexes are preferentially attacked at the least hindered position giving rise to linear products, as illustrated with several ( E )‐configured allylic substrates. Under isomerization free conditions the branched products are formed preferentially from the corresponding ( Z )‐allyl substrates. An interesting behavior is observed in the reaction of secondary allylic substrates. Aryl‐substituted substrates show a significant memory effect which can be explained by an asymmetric π‐allyl complex. For alkyl‐substituted substrates a strong dependence of the regioselectivity on the leaving group is observed, which can be explained by different conformations in the ionization step. Under isomerization free conditions the product ratio gives important information about this step.