Lewis acids overview

In summary, the work in this thesis provides an overview of what can be achieved with Lewis-acid and micellar catalysis for Diels-Alder reactions in water as exemplified by the reaction of3-phenyl-l-(2-pyridyl)-2-propene-l-ones with cyclopentadiene. Extension of the observed beneficial effect of water on rates and particularly enantioselectivities to other systems is envisaged. 

W. B. Jensen, The Lewis Acid-Base Concepts, An Overview, John Wiley Sons, Hoboken, NJ, 1980. 

Manson (72,) expanded the concept to the solid state by observing that the strength of composite materials also depended upon the acid-base interaction between continuous and dispersed phases. More directly, Vanderhoff et al. (21) addressed the issue of adhesion of polymeric materials to corroded steel. They synthesized eight corrosion products of iron, and used the interaction scheme developed by Fowkes and Manson first to characterize the iron corrosion products as Lewis acids or bases and then to select polymer vehicles for practical coating systems. Such results were employed to enhance the adhesion of epoxy systems to substrates which were predominantly iron oxide in nature. A good overview of these Issues was presented by Fowkes in 1983 (74). ... 

This overview impressively demonstrates that Bi(III) salts are not only versatile Lewis acid catalysts for the activation of cr-donors, including benzyl and propargyl alcohols, but also efficient catalysts for the activation of Ji-donors such as styrenes or alkynes. In recent years, various environmentally benign bismuth-catalyzed methods have been developed for the alkylation of arenes, heteroarenes,... 

Polyfluorooxiranes rearrange to carbonyl compounds in the presence of a wide range of catalysts. The nature of the product carbonyl compound depends on the structure of the epoxide and the catalyst an overview is given in Scheme 8. Monosubstituted perfluorooxiranes generally give acyl fluorides with Lewis bases, and trifluoromethyl ketones with Lewis acids. Symmetrically 2,3-disubstituted perfluorooxiranes give ketones with either Lewis acids or Lewis bases. In the presence of Lewis acids, unsymmetrically 2.3-disubstituted perfluorooxiranes give a 1 1 mixture of the two possible ketones. 

Asymmetric Mannich reactions provide useful routes for the synthesis of optically active p-amino ketones or esters, which are versatile chiral building blocks for the preparation of many nitrogen-containing biologically important compounds [1-6]. While several diastereoselective Mannich reactions with chiral auxiliaries have been reported, very little is known about enantioselective versions. In 1991, Corey et al. reported the first example of the enantioselective synthesis of p-amino acid esters using chiral boron enolates [7]. Yamamoto et al. disclosed enantioselective reactions of imines with ketene silyl acetals using a Bronsted acid-assisted chiral Lewis acid [8]. In all cases, however, stoichiometric amounts of chiral sources were needed. Asymmetric Mannich reactions using small amounts of chiral sources were not reported before 1997. This chapter presents an overview of catalytic asymmetric Mannich reactions. 

Following up this initial work a large number of reactions have been published by academic and industrial groups wherein a Lewis-acidic chloroaluminate ionic liquid is used as the acidic catalyst. A comprehensive overview on these research activities can be found in several reviews on this topic and the literature cited therein [18, 22, 37]. 

Variations on this overview conceptualization occur because of differing isomorphic substitution patterns in 2 1 clay minerals. For example, both Li- and Na-vermiculite can form mono- and bilayer hydrates, whereas K-, Rb-, and Cs-vermiculite cannot. For the latter, inner-sphere surface complexes are stable against solvation of the cations because of the softer Lewis acid character of the latter and a favorable siloxane-surface stereochemistry [23]. 

Jensen, W. B. The Lewis Acid-Base Concept — an Overview. New York Wiley 1980... 

W. B. Jensen, The Lewis Acid-Base Concepts An Overview, Wiley-Interscience, New York, 1980, and H. L Finston and Allen C. Rychtman, A New View of Current Acid-Base Theories, John Wiley Sons, New York, 1982, provide good overviews of the history of acid-base theories and critical discussions of the different theories. R. G. Pearson s Hard and Soft Acids and Bases, Dowden, Hutchinson, Ross, Stroudsburg, PA, 1973, is a review by one of the leading exponents of HSAB. For other viewpoints, the references provided in this chapter should be consulted. 

The design of novel Lewis acidic reagents for additions to nonconjugated carbonyls, based on structural information, has attracted much attention in recent years. An excellent overview of this subject has recently appeared, in which the mechanistic aspects of and various models for carbonyl addition processes are Wghlighted. In particular, attention was directed towards the ab initio treatment of solvation effects in additions to the carbonyl group. 37 These calculations indicated that in the addition of water... 

In this chapter, our research on use of the Lewis acid catalysts in carbon-carbon bond-forming reactions in aqueous solvents is overviewed. 

The concept of active sites has helped explain catalysis by enzymes and coenzymes. Although surface functional groups are less specific than enzymes, they form an array of surface complexes whose reactivities determine the mechanism of many surface-controlled processes. Many mechanisms can be described readily in terms of Br0nsted acid sites or Lewis acid sites. Of course, the properties of the surfaces are influenced by the properties and conditions of the bulk structure, and the action of special surface structural entities will be influenced by the properties of both surface and bulk. List I gives an overview of the major concepts and important applications. 

In this chapter, an overview of the electrophilic snbstitntion chemistry of allyltin compounds leading to the formation of a new C—C bond is presented. Mechanistic considerations and a synopsis of information derived from detailed studies of allyltin reactions develop a perspective, which serves as a guide for planning new reactions. The major emphasis of the chapter is devoted to Lewis acid-promoted allylation reactions of aldehydes and related species. 

Jensen, W.B. (1980) The Lewis Acid-Base Concepts An Overview, Wiley, New York, USA. 

This paper presents a comprehensive overview of heterogeneously catalysed MPVO reactions. It includes the recent application of zeolites as new recycleable solid catalysts for the MPVO reaction. The activity of these catalysts is related to their Lewis acid and/or basic properties. Some remarkable examples of shape-selective conversions resulting in high stereoselectivities have recently been found by our group. 

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