N-Tosylhydrazones: versatile synthons in the construction of cyclic compounds.

N-Tosylhydrazones have recently emerged as useful synthons in a variety of transition-metal-catalyzed and transition-metal-free reactions, which affords novel methodologies for the formation of carbon-carbon and carbon-heteroatom bonds. In this context, it has been found that N-tosylhydrazones can be used as versatile building blocks in the construction of a range of cyclic compounds. In this review, cyclization reactions based on N-tosylhydrazones as substrates are discussed. A series of cyclic compounds, including aromatic and non-aromatic ring systems, are demonstrated to be easily constructed by cyclizations with N-tosylhydrazones.