IntroductionCyclodextrins (CDs) are naturally occurring torus -shaped molecules composed of 6, 7, or 8 D -glucose units. A fascinating property of CDs is their ability to incorporate other organic compounds into their cavities in aqueous solution. 1 Since their discovery, CDs have served as prototypes for novel host compounds and catalysts. The use of CDs as microvessels to perform chemical reactions has attracted the interest of chemists since the 1960s. 2 Effects of CDs on reactions are mainly divided into two categories. The fi rst effect is the catalytic effect, designated as the ' enzyme model. ' CD and the reactant initially form a CD -reactant reaction intermediate involving a covalent bond, which then proceeds to product. The second effect does not involve a covalent bond. The cavity of CD presents a new reaction environment to the reactant, an ' extra reaction fi eld ' , in which the reactivity, such as rate or selectivity, changes. In these cases, the role of the CD does not always catalyze, but mediates the reaction. The CD cavity is less polar than the bulk aqueous medium. The permittivity in the CD cavity is known to be nearly the same as that of dioxane. The microenvironment around the reactant in the CD cavity is different from that in the reaction media. Three distinct microenvironmental effects are expected: a) microsolvent effects, b) the protection of unstable intermediates or products, and c) the solubilization of the reactant. In addition, conformational effects can also be expected:
Molecular Encapsulation: Organic Reactions in Constrained SystemsEdited by Udo H. Brinker and Jean-Luc Mieusset