ABSTRACT
This chapter illustrates some of the concepts of the use of cyclic systems. The use of Baldwin’s rules for the formation of cyclic systems can rationalize many of the ring-forming reactions Cyclization reactions have been omitted when the product’s steric requirements are the overriding factors, such as a cis-cyclopropane in a polycyclic system, and allow for no flexibility in the approach. Intramolecular cyclization is a useful method for the preparation of lactones and cyclic ethers. The most common examples are iodolactonization and iodoetherification, the difference being that the former uses a carboxylic acid derivative as the nucleophile, while the latter relies on a hydroxy group. A number of the methods developed for five-membered ring compounds can be used with six-membered rings. These methodologies include the chemistry of lactol ethers and vinyl ethers. The cyclic system itself often provides considerable control over relative stereochemistry.
