Asymmetric catalysis of carbonyl-ene reactions and related carbon-carbon bond forming reactions

The chiral titanium complexes (BINOL-TiX(2)), prepared in situ from (i-PrO)(2)TiX(2) (X=Br or Cl) and an optically pure binaphthol (BINOL) in the presence of molecular sieves 4A (MS 4A), serve as efficient enantioselective catalysts for glyoxylate-ene reactions to afford the a-hydroxy esters in high % ee's. The specific role of MS 4A and the structure of actual catalytic species are discussed. The most striking is the observation of positive non-linear effect (asymmetric amplification) that the catalyst derived from BINOL of ca. 40% ee affords the product of >90% ee. The BINOL-derived titanium catalysts work well for other carbon-carbon bond forming reactions such as the Mukaiyama aldol reactions, the (hetero) Diels-Alder reactions, and allylmetal-carbonyl addition reactions.