Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• ][42][43][44][45][46], azulenes and their homologous compounds [32][47][48][49][50][51][52][53][54][55][56][57][58], boron dipyrromethenes (BODIPYs) [41][59][60][61], porphyrins [62][63][64], chlorophylls [65][66], triazenes [67][68], ynamides [69][70][71], arylynamines [72], indoles [73], and γ

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• connectivity through the seven-membered ring of azulene. The key precursors required in this synthesis, 4,7-dibromo-6-(n-alkyl)azulenes 12–14 were synthesized by treating 2,5-dibromo-3-alkylthiophenes 6–8 with HOF·CH3CN followed by reaction with dimethylaminofulvene (Scheme 4). The synthesis of 4,7-diethynyl-6

• resonance signals when compared to free azulenes. The absorption and electrochemical studies conducted on these complexes 40–43 revealed that their properties could be tuned by varying the ruthenium content in the polymer. A higher ruthenium content was inducing a larger blue-shift of the absorption bands

• contrast. Azulene-methacrylate copolymers Emrick and co-workers [45] reported the synthesis of azulene-substituted methacrylate polymers derived from a free radical polymerization strategy, where azulenes were used as pendants. The key starting points to make these polymers were azulene-2-yl methacrylate

Calixazulenes: azulene-based calixarene analogues – an overview and recent supramolecular complexation studies

• Paris E. Georghiou,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Hidetaka Nishimura,
• Jaehyun Lee,
• Atsushi Wakamiya and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2018, 14, 2488–2494, doi:10.3762/bjoc.14.225

• -hydrocarbon calix[4]azulenes which have been synthesized in good yields by their method. This allowed studying their supramolecular properties. This report is of our latest work on the solution-state supramolecular complexation of one of these calix[4]azulenes, namely tetrakis(5,7-diphenyl)calix[4]azulene or

• “OPC4A”, with several electron-deficient tetraalkyammonium salts. As a result of more recent methods developed by us and others employing Suzuki–Miyaura cross-coupling reactions to produce additional functionalized azulenes, the promise of further greater functionalized calixazulenes lies in store to be

• . Since these three calix[4]azulenes 3–5 are all-hydrocarbon compounds they differ significantly from the better-studied calix[4]arenes, which usually have some heteroatoms such as oxygen, nitrogen or sulfur in their structures. As a consequence, compounds 3–5 have solubility limitations. Furthermore, the

On the bromination of the dihydroazulene/vinylheptafulvene photo-/thermoswitch

• Virginia Mazzanti,
• Martina Cacciarini,
• Søren L. Broman,
• Christian R. Parker,
• Magnus Schau-Magnussen,
• Andrew D. Bond and
• Mogens B. Nielsen

Beilstein J. Org. Chem. 2012, 8, 958–966, doi:10.3762/bjoc.8.108

• fully unsaturated species. Azulenes were also found to form from brominated compounds when left standing for a long time in the solid state. Kinetics measurements reveal that the 3-bromo substituent enhances the rate of the thermal conversion of the VHF to DHA, which is opposite to the effect exerted by

• products. This product is not surprising, inasmuch as we have previously found that a solution of the related dibromide 3 over time underwent conversion to a mixture of 1-bromo-3-cyano-2-phenylazulene and 1-cyano-2-phenylazulene [5]. The conversion of 13 into azulenes was, however, so fast that we could

• not perform the controlled elimination of HBr by LiHMDS to generate the corresponding 7-bromo-DHA as we could from 3. The structure of the azulene 14 was confirmed by X-ray crystallographic analysis (Figure 3c). Functionalized azulenes are themselves interesting in materials chemistry for their

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

• Zakir Hussain,
• Henning Hopf,
• Khurshid Ayub and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

• approach was reported previously [5]. Recently, a new synthetic method for the construction of a hydroazulene skeleton by a [5 + 2]cycloaddition reaction was also developed [6]. Additionally, there have been many reports on the synthesis of 2,6-disubstituted azulenes [7][8]. In 1951, the ring expansion of

• azulenes (giving a bluish color). Similar to our earlier investigations [10], various isomers could be formed through the rearrangement of double bonds in the seven-membered ring of 7. However, through the NMR data of 7, we saw the formation of an isomer with double bonds at the ring junction as a major

• temperature for a few days, they form the corresponding azulenes. Such an unusual behavior of compounds 9 and 10 can easily be attributed to their oxidation. Additionally, our earlier investigations on similar compounds [10][13] showed that fully hydrogenated derivatives show pronounced mesogenic behavior

One-pot four-component synthesis of pyrimidyl and pyrazolyl substituted azulenes by glyoxylation–decarbonylative alkynylation–cyclocondensation sequences

• Charlotte F. Gers,
• Julia Rosellen,
• Eugen Merkul and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2011, 7, 1173–1181, doi:10.3762/bjoc.7.136

• - and pyrazolylazulenes through the use of glyoxylation–decarbonylative alkynylation–cyclocondensation sequences starting from azulene or guaiazulene as substrates, gives rise to the formation of the target compounds in moderate to good yields. Keywords: azulenes; catalysis; decarbonylation

• chemistry has recently been reported [39]. N-Heteroaryl-substituted azulenes can be accessed by stoichiometric [40][41] as well as Pd-catalyzed cross-coupling processes [42][43][44]. However, these methods have only delivered a narrow range of derivatives. Prior to application in Pd-catalyzed processes

• , azulenes must be functionalized, either by halogenation or borylation, and some of these derivatives were found to be quite unstable [45][46]. To the best of our knowledge, no diversity-oriented multicomponent syntheses of azulenyl heterocycles have been reported so far. Here, we report the development of