Highly enantioselective carbonyl-ene reaction catalyzed by chiral titanium complexes: Toward structural elucidation of catalytically active species

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Abstract

We have developed highly enantioselective carbonyl-ene reactions catalyzed by a chiral titanium complex prepared from optically pure binaphthol (BINOL) and (i-PrO)2TiCl2 in the presence of molecular sieves (MS) 4 A. During the course of the structural elucidation of catalytically active "BINOL-Ti", MS 4 A employed in the catalyst preparation step was found to function not only as a base to trap HCl but also as H2O donor eventually providing the active "BINOL-Ti". The effect of counter cations of zeolites was also investigated in the catalyst preparation step. A sufficient content of Na cation in the zeolites is the key for efficient formation of the active "BINOL-Ti". Direct transformation of BINOL-Ti(Oi-Pr)2 under the influence of the hydrated MS 4 A into the active catalyst was examined, where BINOL-Ti(Oi-Pr)2 was assembled into the active "BINOL-Ti" primarily composed of μ3-oxo (Ti3O) species via the di-μ3-oxo bridging tetranuclear titanium complex. Although the exact structure of the active "BINOL-Ti" has not yet been determined, we proposed a plausible pathway to the formation of active "BINOL-Ti" from BINOL and (i-PrO)2TiCl2 under the influence of hydrated MS 4 A.

Original languageEnglish
Pages (from-to)748-760
Number of pages13
JournalYuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry
Volume65
Issue number8
DOIs
Publication statusPublished - 2007 Aug

Keywords

  • Asymmetric catalysis
  • Binaphthol
  • Enantioselective
  • Ene reaction
  • Lewis acid
  • Molecular sieves
  • Titanium
  • Zeolite

ASJC Scopus subject areas

  • Organic Chemistry

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