1,4-Conjugate Addition of Aryl boronic Acids on Cyclohexenone as Catalyzed by Rhodium(I) Complexes of C2-Symmetric Bioxazoline Fused N-heterocyclic Carbenes

Balasubramaniyam Ramasamy, A.P. Prakasham, Manoj Kumar Gangwar, Prasenjit Ghosh (Corresponding author)

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9 Citations (Scopus)

Abstract

Rhodium(I) complexes (1-3) of chiral C2-symmetric tricyclic bioxazoline fused imidazole derived N-heterocyclic carbene ligands were efficient precatalysts for the 1,4-conjugate addition of aryl boronic acids to cyclohexenone yielding 3-aryl cyclohexanones in moderate to excellent yields but without any chirality transfer. Quite significantly, the intermediates of the proposed catalytic cycle namely, a rhodium hydroxo species (A), a phenyl bound rhodium species (B) and a 3-phenyl cyclohexenolate bound rhodium species (D) have been detected by mass spectrometry. Lastly, the rhodium(I) precatalysts of the type, {(3R,7R)-3,7-di-R-2,3,7,8-tetrahydrodioxazolo[3,2-c:3′,2′-e]imidazol-5-ylidene}Rh(COD)Cl, [R=s-butyl (1), i-butyl (2), i-propyl (3), COD=1, 5-cyclooctadiene] were prepared by the direct metalation of tricyclic oxazoline fused imidazole derived N-heterocyclic carbene precursors namely, (3R,7R)-3,7-di-R-2,3,7,8-tetrahydrodioxazolo[3,2-c:3′,2′-e]imidazol-4-ium trifluoromethanesulfonate, [R=s-butyl, i-butyl, i-propyl] with {(COD)RhCl}2 in presence of t-BuOK at room temperature.

Original languageEnglish
Pages (from-to)8526-8533
Number of pages8
JournalChemistrySelect
Volume4
Issue number29
DOIs
Publication statusPublished - 7 Aug 2019
Externally publishedYes

Bibliographical note

Funding Information:
We thank BASF India and the Department of Science and Technology (EMR/2014/000254), New Delhi, India, and Council of Scientific & Industrial Research (CSIR) {01(2880)/17/EMR‐II} New Delhi, for the financial support of this research. We gratefully acknowledge the Single Crystal X‐ray Diffraction Facility at the Department of Chemistry, IIT Bombay, India for the crystallographic characterization data. B.R. thanks BASF India and A.P.P, and M.K.G. thank CSIR, New Delhi, India, for the research fellowships

Funding

. We thank BASF India and the Department of Science and Technology (EMR/2014/000254), New Delhi, India, and Council of Scientific & Industrial Research (CSIR) {01(2880)/17/EMR‐II} New Delhi, for the financial support of this research. We gratefully acknowledge the Single Crystal X‐ray Diffraction Facility at the Department of Chemistry, IIT Bombay, India for the crystallographic characterization data. B.R. thanks BASF India and A.P.P, and M.K.G. thank CSIR, New Delhi, India, for the research fellowships We thank BASF India and the Department of Science and Technology (EMR/2014/000254), New Delhi, India, and Council of Scientific & Industrial Research (CSIR) {01(2880)/17/EMR-II} New Delhi, for the financial support of this research. We gratefully acknowledge the Single Crystal X-ray Diffraction Facility at the Department of Chemistry, IIT Bombay, India for the crystallographic characterization data. B.R. thanks BASF India and A.P.P, and M.K.G. thank CSIR, New Delhi, India, for the research fellowships.

Keywords

  • 1,4-conjugate addition
  • aryl boronic acids
  • bioxazoline fused imidazole rings
  • C-symmetry α,β-unsaturated ketone
  • N-heterocyclic carbene
  • rhodium

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