Dancing with Azulene

Abstract

It seems interesting to adopt the idea of dance in the context of the arrangement of molecular blocks in the building of molecular systems. Just as various dances can create various feelings, the nature and arrangement of molecular blocks in the generated molecular system can induce different properties. We consider obtaining such “dancing” systems in which the still little-known azulene moieties are involved. The dark blue nonbenzenoid aromatic azulene has one less axis of symmetry relative to the two axes of its isomer, i.e., the fully benzenoid naphthalene, acquiring valuable properties as a result that can be used successfully in technical applications. In a dancing system, the azulene moieties can be connected directly, or a more or less complex spacer can be inserted between them. Several azulene moieties can form a linear oligomer or a polymer and the involvement of azulene moieties in nonlinear molecules, such as crown ethers, calixarenes, azuliporphyrins, or azulenophane, is a relatively new and intensely studied topic. Some aspects are covered in this review, which are mainly related to obtaining the mentioned azulene compounds and less to their characterization or physico-chemical properties.

Azulene, Reactivity, and Scientific Interest Inversely Proportional to Ring Size; Part 1: The Five-Membered Ring

“…The purpose of this subchapter is to present azulenes cross-coupling reactions. Unlike the published reviews that target this very field [11,[15][16][17]20,21], our goal will be the reactions that take place at the five azulene ring. As already written, the presentation is mostly graphic with schemes including the reaction conditions and yields, and where considered necessary, the proposed reaction mechanisms are presented.…”

“…From the large amount of information that has been published, only a few examples are selected that are presented as reactions in Scheme 64 with the specification of the reaction conditions and the yields obtained. Many efforts have been focused on the investigation of calixarene, azulenophane and azuliporphyrin, and two reviews have recently appeared regarding this topic [17,21]. Therefore, to complete the information on the behavior of the azulene five ring, only a few examples from these classes of compounds will be given.…”

“…The acid-catalyzed reaction affords as major product a polymer with only a low proportion of calixarene [112,113]. Many efforts have been focused on the investigation of calixarene, azulenophane and azuliporphyrin, and two reviews have recently appeared regarding this topic [17,21]. Therefore, to complete the information on the behavior of the azulene five ring, only a few examples from these classes of compounds will be given.…”

“…The paper of Zhuang et al [12] presents the synthesis of azulene-based aromatic compounds for optoelectronic and energy applications. Razus et al recently published a number of reviews on the obtaining of azulenes [11,[19][20][21], Elhawy's article from 2021 discussed the synthesis of azulene derivatives through Pd-catalyzed coupling techniques [22] and Gao condensed information about the applications of azulene-based π-functional materials [23]. From this, it follows that most of these papers were directed towards particular and welldefined targets, for example, certain classes of compounds, synthesis routes, technical uses, etc.…”