Acid catalysis future research

In Chapter 6 we survey what has been accomplished and indicate directions for future research. Furthermore, we critically review the influence of water on Lewis acid - Lewis base interactions. This influence has severe implications for catalysis, in particular when hard Lewis acids and bases are involved. We conclude that claims of Lewis-acid catalysis should be accompanied by evidence for a direct interaction between catalyst and substrate. 

In this paragraph it was demonstrated that Lewis acid catalysis can be extended to aqueous media. Although water is likely to alter the complexation step, the use of Lewis acids is not restricted to organic solvents. Most importantly, the advantageous effects of Lewis acid catalysis and water are often additive. Since the development of catalytic systems which are water-tolerant or even benefit from the presence of water is still in its infancy, these results are highly promising and open new avenues for future research. 

A screen of chiral Lewis acids was carried out by Jorgensen, but this effort failed to reveal any effective enantioselective catalysts [31]. However, very recently Wulff disclosed an extremely exciting result in the VAPOL-BH3 catalyzed reaction between ethyl diazoacetate and imines (Scheme 14) [32]. Although the details had not been published at the time this chapter was written, it seems likely that this method will constitute an important breakthrough and establish a new direction for future research in the field of asymmetric aziridination catalysis. 

The utilization of copper(I) catalysis in asymmetric transformations is universal due to the special valence electron, Lewis acidity, and coordination characteristic of the metal. Copper salts are easily available, cost-efficient, and nontoxic. Copper(l)-catalyzed asymmetric cycloaddition and cascade addition-cyclization reactions are straightforward methodologies for the stereoselective construction of various biologically and medicinally important heterocyclic compounds. In the past 5 years, main endeavors have been paid into catalytic asymmetric [3+2] cycloadditions other types of cycloaddition protocols are relatively less developed. The examples described in this chapter clearly demonstrate the potential of chiral Cu(I) complexes in the synthesis of enantioenriched heterocycles. Further studies may lie in the diversification of catalytic system, reaction type, and catalysis mode. Research in this field is still challenging and highly desirable, and it would be expected that more discoveries will come in the near future. 

The three themes of the symposium selective hydrogenation, selective oxidation and acid-base catalysis were introduced by four plenary lectures and two invited communications. A panel concerned with the future of zeolites and other shape-selective materials for fine chemical synthesis was conducted by specialists in the field D. Barthomeuf (University of Paris 6), E. Derouane (University of Namur), L. Forni (University of Milan), M. Gubelmann (Rhone-Poulenc, St Fons), W. Hoelderich (BASF, Ludwigshafen) and G. Perot (University of Poitiers). An exhibition of equipment was held during the symposium on October 3 and 4. Over 20 firms exhibited equipment, chemicals and catalysts which were of interest to researchers involved with the synthesis of functional compounds by heterogeneous catalysis. 

The synthesis of pyridine bases with solid-acid catalysts is of considerable commercial importance. In the future, zeolites and related catalysts can be expected to have an impact on other areas of heterocyclic chemistry, because they bring the combined benefits of high yields and environmentally clean processes. The use of these catalysts to introduce new functions into pre-formed heterocycles or to manipulate their side chains-a topic not addressed here-is an area worthy of more research activity. Hopefully, this brief review provides some insight into heterocyclic chemistry and encourages readers to pursue their own catalysis research in this fascinating and fruitful area. 

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