H-2-quadrupolar coupling-based analysis of stereochemical and regiochemical memory in the Pd-catalysed allylic alkylation of iso-cinnamyl type substrates employing the chiral monophosphine ligands 'MOP' and 'MAP'

L Gouriou, GC Lloyd-Jones*, S Vyskocil, P Kocovsky

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The reaction of iso-cinnamyl acetate with NaC(Me)(CO2Me2), catalysed by Pd-'MOP' (MOP = 2-methoxy-2'-diphenylphosphino-1,1'-binaphtlialene) is known to proceed with a regiochemical memory effect that results in the predominant generation of the branched alkylation product. The analogous reaction employing 'MAP' as ligand (MAP = 2-N,N-dimethylamino-2'-diphenylphosphino-1,1'-binaphthalene) proceeds with 'normal' regio selectivity to generate predominantly the linear isomer of product. A H-2-NMR based analysis, employing quadrupolar coupling in a chiral liquid crystal matrix, has been developed to facilitate the simultaneous study of the regiochemical and stereochemical outcome of the reaction of both enantiomers of iso-cinnamyl ester substrates in H-2-labelled but racemic samples. The analysis allows the comparison of relative rates of two competing isomerisation processes occurring in the pi-allyl intermediates in the Pd-catalysed reaction, one of which facilitates asymmetric induction, the other resulting in loss of regiochemical memory. It is demonstrated that the two processes are partially coupled and that this then limits the attainment of high global enantiomeric excess in the branched product to reactions that proceed with low regiochemical retention. A key factor for the observation of high regiochemical memory is found to be the nucleophilicity of the malonate anion and the electrophilicity of the Pd-pi-allyl intermediate with reduction in the reactivity of either partner resulting in the onset of substantial loss of memory. (C) 2003 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)525-537
Number of pages13
JournalJournal of organometallic chemistry
Volume687
Issue number2
DOIs
Publication statusPublished - 7 Dec 2003

Keywords

  • palladium
  • asymmetric catalysis
  • memory effects
  • H-2-NMR
  • liquid crystals
  • ASYMMETRIC CATALYSIS
  • HOMOGENEOUS CATALYSIS
  • KINETIC RESOLUTION
  • PALLADIUM
  • COMPLEXES
  • COORDINATION
  • SUBSTITUTION
  • PHOSPHINOOXAZOLINES
  • REGIOCONTROL
  • AMINATION

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