Cyclodextrins as Promoters in Aqueous Organic Synthesis

The ever-increasing demand for environmentally benign and clean synthetic processes combined with high selectivities led to organic synthesis in water mimicking biochemical selectivity involving host guest complexes. Amongst various possibilities, cyclodextrin (CDs) possessing hydrophobic cavities have acquired significance as they promote organic reactions in water leading to high selectivities. The microenvironment around the substrate in the CD cavity makes it different from the classical reaction medium, protecting the substrate, controlling its orientation and conformation, accommodating only those molecules which fit the size of the particular CD cavity, and promoting the reaction through participation of its functionalities. Some of the applications of CDs to attain high selectivities in a variety of organic reactions such as nucleophilic opening of oxiranes, Strecker & Michael reactions, oxidations, allylations, synthesis of heterocycles, chiral discrimination etc. are discussed.