Developing the Saegusa-Ito cyclisation for the synthesis of difluorinated cyclohexenones

Jonathan M. Percy, Adam W. McCarter, Alan L. Sewell, Nikki Sloan, Alan R. Kennedy, David J. Hirst

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Abstract

Palladium(II)-catalysed cycloalkenylation (Saegusa-Ito cyclisation) has been used for the first time to transform difluorinated silylenol ethers to difluorinated cycloalkenones under mild conditions. The silylenol ether precursors were prepared in two high-yielding steps from trifluoroethanol, and cyclised in moderate to good yields. A combination of air and copper(I) chloride in acetonitrile achieved the turnover of the initial palladium(II) salt, while the provision of an oxygen atmosphere ensured more rapid reaction. Annulations required a minimum level of substitution on the chain, but failed when the alkene was substituted. Annelations allowed a range of n,6-bicyclic systems to be prepared and afforded three products in which heterocycles were fused to the new cyclohexenone. The least substituted system explored underwent cyclisation followed by terminal oxidation to a cyclic enal, which corresponded to a Wacker product of unusual regiochemistry.
Original languageEnglish
Pages (from-to)19119–19127
Number of pages9
JournalChemistry - A European Journal
Volume21
Issue number52
Early online date13 Nov 2015
DOIs
Publication statusPublished - 21 Dec 2015

Keywords

  • difluoroketone
  • homogeneous catalysis
  • cyclisation
  • palladium
  • oxidation

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