Chirality control in planar chiral cobalt oxazoline palladacycles

Doyle J. Cassar, Hemin Roghzai, Didier Villemin, Peter N. Horton, Simon J. Coles, Christopher J. Richards

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8 Citations (Scopus)
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Abstract

Palladation of (eta(5)-(S)-2-(4-R-substituted)-oxazolinylcyclopentadienyl)(eta(4)-tetraphenylcyclobutadiene)cobalt-(I) with Pd(OAc)(2) (R = Me, CH2Cy, CH(2)i-Pr, CH2Ph) resulted exclusively in formation of the (S,Sp)-palladacycle with R = CH2Cy (acetic acid solvent) and up to 13:1 selectivity in favor of the (S,Sp)-palladacycle with R = CH(2)i-Pr (CH2Cl2 solvent). In the latter case diastereomeric purity was achieved by recrystallization, and the absolute configuration of the new element of planar chirality was established by X-ray crystallography. These outcomes contrast with the opposite sense of diastereoselectivity observed for the corresponding R = i-Pr-substituted oxazoline, which results in the palladacycle (S,R-p)-COP-OAc (acetic acid solvent), these palladation reactions being under either kinetic (S,S-p) or thermodynamic (S,Rp) control. Following conversion to the chloride-bridged (S,S-p)-palladacycle dimer (R = CH2Cy), this was employed as a catalyst for the rearrangement of allylic trichloroacetimidates (0.25 mol % catalyst loading, up to 80% ee).

Original languageEnglish
Pages (from-to)2953-2961
Number of pages9
JournalOrganometallics
Volume34
Issue number12
Early online date28 May 2015
DOIs
Publication statusPublished - 22 Jun 2015

Keywords

  • CATALYTIC ASYMMETRIC-SYNTHESIS
  • DIASTEREOSELECTIVE ORTHO-LITHIATION
  • AZA-CLAISEN REARRANGEMENT
  • ALLYLIC ESTERS
  • DIRECT ARYLATION
  • DERIVATIVES
  • LIGANDS
  • PALLADATION
  • MECHANISM
  • HETEROCYCLES

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