Ring Closure Reactions in Heterocyclic Systems with Implementation of Wittig and aza-Wittig Reactions

Applications of Wittig and aza-Wittig reactions in various cyclizations reported during the past ten years are reviewed. The relevant literature is classified into two categories according to these two main approaches and, in both sections, the chemistry is exemplified according to the ring types synthesized. The chemical examples include both intramolecular ring closures and multistep procedures. Within the aza-Wittig reactions, special attention is paid to those products that can undergo electrocyclization to yield nitrogen heterocycles (e.g. pyridines or pyrimidines). In most interesting cases, the reaction mechanism of the transformations is discussed.