A Century of Azulene Chemistry; A Brief Look at Azulenes Building

The target of this review is to familiarize researchers from the field, especially for those who want to find out information about the synthesis pathways of azulenes. The properties of the azulene system are very different from those of its isomer, naphthalene. This difference is a consequence of the monoaxial symmetry of azulene geometry and its non-alternating aromatic structure as opposed to the biaxial symmetry and benzenoid structure of naphthalene. The processing of the information from the literature on azulene synthesis is based on the raw materials from which the procedures start. In many cases, instead of the description of reaction pathways, presentation in the form of schemes was preferred, in which the steps and reaction conditions chosen for them, as well as the yields obtained, were highlighted.