Multifunctional Asymmetric Catalysis
The development of catalytic asymmetric reactions is one of the major areas of research in the field of organic chemistry. So far, a number of chiral catalysts have been reported, and some of them have exhibited a much higher catalytic efficiency than enzymes, which are natural catalysts (Herrmann and Cornils 1996; Noyori 1994; Ojima 1994; Bosnich 1986; Morrison 1985). Most of the synthetic asymmetric catalysts, however, show limited activity in terms of either enantioselectivity or chemical yields. The major difference between synthetic asymmetric catalysts and enzymes is that the former activate only one side of the substrate in an intermolecular reaction, whereas the latter not only activate both sides of the substrate but can also control the orientation of the substrate. If this kind of synergistic cooperation can be realized in synthetic asymmetric catalysis, the concept will open up a new field in asymmetric synthesis, and a wide range of applications may well ensue. This minireview covers two types of asymmetric two-center catalyses promoted by complexes showing Lewis acidity and Br0nsted basicity and/or Lewis acidity and Lewis basicity (Steinhagen and Helmchen 1996; Shibasaki et al. 1997).
KeywordsPhosphine Oxide Aldol Reaction Heterobimetallic Complex Aldol Product Trimethylsilyl Cyanide
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