Seven-membered Rings with Three Heteroatoms 1,3,5

Abstract

This chapter reviews the literature data on properties, reactivity, and ring synthesis of seven-membered ring heterocycles with 1,3,5-heteroatoms (triazepines, trioxepins, trithiepins, oxadiazepines, dioxazepines, thiadiazepines, dithiazepines, and oxathiazepines) including their fused and bridged derivatives, such as homotriazaadamantanes, anhydronucleosides, and hexaazaisowurtzitanes, published since 1994. To provide the comprehensive coverage of the material, a number of earlier references, not included in CHEC(1984) and CHEC-II(1996), are also cited. The most important reactions of this type of compounds are heterocyclic ring transformations, namely, the thermal or photochemical ring contraction and nucleophilic ring opening, the latter being particularly well studied for various anhydronucleosides containing dioxazepine or oxadiazepine heterocyclic rings. The other reactions not affecting the seven-membered ring, such as ring heteroatom modifications, are also discussed. A wide variety of synthetic methods have been used for the formation of a triheteropine ring: from intramolecular cyclization, applied to the synthesis of monomolecular, fused and bridged (such as anhydronucleosides) compounds, to multicomponent condensation and ring expansion reactions. Of the two-component cyclizations, classified by the number of the atoms provided for the ring construction by each component, the [3+4] cyclocondensations are the most popular for the synthesis of various monocyclic and benzo- and heterocycle-fused derivatives. A short summary of synthetic methods used for the preparation of particular classes of compounds is also given.