Crystallization-induced diastereomer transformations

An overview is given of the use of crystallization-induced diastereomer transformations (CIDT) in organic synthesis. Examples are presented under two main classes of CIDT: those in which the equilibrating and directing centers reside on different counterions of a salt and those in which they are part of the same covalent backbone. It is shown that the mechanism of equilibration is based on either rotation around hindered bonds or facile cleavage and formation of bonds which are activated in some way. Examples of the latter included proton transfer to/from relatively acidic carbon-hydrogen bonds, facile formation of stabilized carbocations, and degenerate substitution reactions.