Journal article
Memory effects in palladium-catalyzed allylic Alkylations of 2-cyclohexen-1-yl acetate
The objective of this work was to characterize the enantiospecificity of the allylic alkylation of enantioenriched 2-cyclohexen-1-yl acetate with the enolate ion of dimethyl malonate catalyzed by unsymmetrical palladium catalysts. The precatalysts employed were (eta(3)-allyl)PdLCl, where L is a mono-phosphine ligand [PPh3, PCy3, P(2-BiPh)Cy-2, or P(t-Bu)(3)], all of which afforded enantiospecificity to some extent (5-47 %).
Quantum mechanical calculations show that, theoretically, the enantiospecificity should be high due to a preference for the "trans to P" transition state in both formation of the eta(3)-allyl intermediate and nucleophilic attack. However, the observed enantiospecificity is relatively low due to isomerization of the eta(3)-allyl intermediate and/or dynamic equilibria between the catalytically active (eta(3)-allyl)PdLCl species and [(eta(3)-allyl)PdL2](+) or [(eta(3)-allyl)PdCl](2).
It was also observed experimentally that increasing the bulk of the phosphine inhibits formation of the [(eta(3)-allyl)PdL2](+) complexes, significantly increasing the observed enantiospecificity for some of the ligands.
Language: | English |
---|---|
Publisher: | WILEY-VCH Verlag |
Year: | 2007 |
Pages: | 2631-2640 |
ISSN: | 16154169 and 16154150 |
Types: | Journal article |
DOI: | 10.1002/adsc.200700315 |
ORCIDs: | Fristrup, Peter and Tanner, David Ackland |