Synthesis of medium-sized ring lactams

Medium-sized ring lactams (7- to 15-membered) find widespread use in organic chemistry as key intermediates in the synthesis of more complex structures or as core structures in natural product or pharmaceutically important compounds. Until now, the generation of such rings is still a challenge in organic synthesis. During the past decade an increasing interest has focused on the generation of cyclic peptides as well as hairpin and beta -turn mimics and the medium-sized rings were thought to represent suitable fragments. Furthermore, a range of complex natural products is characterized by such lactam structure and their total synthesis is a broad field for organic chemists to test new strategies and to develop new methods. The aim of the present chapter is to discus some modern strategies to synthesize seven- to fifteen-membered ring lactams, the scope is restricted to the generation to ring systems bearing a single lactam function. Although the range of reactions described concern only the generation of simple structures without complicated stereogenic properties, most of them seem to bear undiscovered potential with regard to stereoselective synthesis. However, the emphasis of the methods is focused on stereoselective processes. The review is subdivided in three major chapters of ring closure reactions and ring enlargements, additional information is given on cycloadditons and fragmentations.