Seven-Membered Rings

This chapter discusses both fused and non-fused heterocycles, focusing on N, O, and S as the heteroatoms of the seven-membered ring components. The chemistry and biological activities of seven-membered heterocyclic compounds continues to command significant attention. The chapter highlights on research describing the construction of these systems. A continuing trend has been the synthesis of seven-membered derivatives of biologically active molecules, such as carbohydrates and nucleic acids. Many synthetic methods for the synthesis of seven-membered rings are simply the extensions of methodology for the lower homologues; therefore, particular attention has been given to synthetic methods that specifically target the titled systems. Reviews focussing on the featured systems during 2007 have covered the medicinal chemistry of the 1,4-diazepines and the synthesis of macrocyclic shellfish toxins containing spiroimine moieties. Azepine based azasugars are formed from chiral cyclohexyl derivatives, formed from D-(-)-quinic acid, by the oxidative cleavage of a diol or the ozonolysis of an alkene to yield a dialdehyde followed by reductive amination forming the heterocyclic system The tandem-Staudinger-aza Wittig mediated ring expansion of a 6-azido pyranoside is used to yield isofagomine derivatives.