Direct Access to Functionalized Azulenes and Pseudoazulenes via Unconventional Alkyne Cyclization Reactions

Abstract

Owing to the unique chemical structure and photophysical properties of azulene, azulene derivatives show great promise for a wide range of prospective technical applications, such as molecular switching, sensors, solar cells, and biological activities. In addition to functionalization of the existed azulene cores, direct construction of azulenes via condensation with odd‐membered carbocycles such as tropolone, 2‐oxazulanone, cyclopentadiene, and 6‐aminofulvene is another classical method for obtaining azulene derivatives. Although alkynes are widely explored for construction of benzene rings, several unconventional cyclization reactions with alkynes produce azulene, pseudoazulene, or azulenone skeletons. This minireview summarizes these interesting and practical cyclization with a classification based on the function of alkyne in the azulene formation process, aiming at capturing the attention of the scientific community to make efforts in the development of such nonalternant cyclization reactions of alkynes.

Thiopyran-Fused Polycyclic Aromatic Compounds Synthesized via Pt(II)-Catalyzed One-Pot Ring-Expansion and 6-endo Cyclization Reactions

“…S-fused polycyclic aromatic hydrocarbons (PAHs) have gained much attention due to their widespread applications in optoelectronic devices, such as light-emitting diodes, , organic photovoltaics, , and field-effect transistors. , Among various S-containing heterocycles, the five-membered thiophene ring is one of the most representative building blocks. − The fused thiophene ring in PAHs can be simply introduced by locking two single-bond-linked segments with a sulfur atom. − Alternatively, S-fused PAHs can be synthesized via conventional cyclization reactions from thiophene-containing precursors. − For example, 1-ethynyl-2-thienyl-substituted aromatics can be converted to benzo­[ b ]­thiophene undergoing classic 6- endo cyclization reaction with the assistance of transition-metal-based catalysts (Figure a), such as indium, − ruthenium, aurum, and platinum. , In comparison to the abundant synthetic methodologies toward S-fused PAHs containing five-membered thiophene rings, fewer reports have focused on their analogues consisting of six-membered thiopyran rings, − most likely due to their different electronic structures and more challenging syntheses. Since thiopyran-fused PAHs present intriguing optoelectronic properties, − such as near-infrared absorption, low oxidation potential, and high charge carrier mobility, the construction of thiopyran-fused PAHs still remains challenging.…”

Synthesis of Azuleno[2,1-b]quinolones and Quinolines via Brønsted Acid-Catalyzed Cyclization of 2-Arylaminoazulenes

“…In this context, we Azulene is one of the 10π-electron non-benzenoid aromatic hydrocarbons having a fused structure of five-and seven-membered rings. To elucidate the physicochemical properties, especially optical and electrochemical properties, a variety of synthetic methods have been developed for azulene-fused derivatives [17][18][19][20][21][22][23]. However, despite the fact that azulene derivatives fused by several heterocycles, such as pyridine [24], thiophene [25], pyrrole, and furan [26,27], have been reported, the preparation of quinolone-and quinoline-fused derivatives have not been conducted so far.…”

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF3: the case of alkyne hydration. Chemistry vs electrochemistry

“…Alkynes are fundamental starting materials towards more complex organic compounds, widely used both in organic chemistry and in electrochemistry as raw materials for the prepara-tion of different molecules of pharmaceutical and industrial interest [1][2][3][4][5][6][7][8][9]. Among the different organic transformations involving alkynes, their hydration is a well-known and useful reaction in organic chemistry, affording carbonyl compounds based on an atom-economical approach.…”