Azulene formylation

The reaction with disubstituted formamides and phosphorus oxychloride, called the Vilsmeier or the Vilsmeier-Haack reaction,is the most common method for the formylation of aromatic rings. However, it is applicable only to active substrates, such as amines and phenols. An intramolecular version is also known.Aromatic hydrocarbons and heterocycles can also be formylated, but only if they are much more active than benzene (e.g., azulenes, ferrocenes). Though A-phenyl-A-methyl-formamide is a common reagent, other arylalkyl amides and dialkyl amides are also used. Phosgene (COCI2) has been used in place of POCI3. The reaction has also been carried out with other amides to give ketones (actually an example of 11-14),... 

Benzene and naphthalene compounds can be formylated under Vil-smeir conditions. The formyl compounds, with or without isolating, can be condensed with amino arenes to give leuco compounds. In this reaction, the benzhydrol intermediate is not isolated.21,79,84 86 The reaction is generally carried out in an alcohol solvent such as isopropanol, butanol, or pentanol and an acid catalyst such as hydrochloric acid, sulfuric acid, or methanesul-fonic acid.87 Acetic acid can also be used both as catalyst and as the solvent. Urea sometimes is added as catalyst.84,88 Terephthaldehyde reacts with W-diethyl-3-methylaniline89 and substituted azulenes to give a bis-triphenylmethane21 57 and 58, respectively. 

Azulene-substituted methyl cations were prepared as illustrated in Figure 7. The hydro derivatives (7a-d) became good precursors for the methyl cations. These derivatives were readily obtained by the reaction of azulenes 6a-d with 1-formyl compounds 5a-d under acidic conditions. The synthesis of the tri(l-... 

In the case of 1-formyl-azulene and 1-nitro-azulene the addition of the... 

It may be mentioned here that 1-formyl- and 1-acetyl-azulene [241] also offer alternative C/O protonation sites, with two carbon alternatives, C-1 and C-3. Nmr spectra show that, in 1-formylazulene,... 

Azobenzol 4-Formyl- IV/ld, 195 Azulen 3-Acetyl-2-amino-l-cyan-V/2c, 230 Benzimidazol... 

In an analogous manner, we succeeded finally in synthesizing the 5-carbonitrile of the kata-condensed tetracyclic azuleno(l, 2-f)azulene (776) in a 50% yield by condensation of (44) with azulene-2-acetonitrile (149) to the red-violet aminonitrile (174) and smooth thermolysis of it78. The hydrocarbon (176) is the first known member of the theoretical 12 isomeric azulenoazulenes of which considerable stability and aromatic properties are predicted79. Indeed, (7 76) can readily be formylated by dimethylformamide-phosphorylchloride in a typical aromatic-electrophilic substitution to the 1-carbaldehyde (7 77)78. ... 

Kuroda, C., Shimizu, S., Haishima, T., and Satoh, J.Y, Synthesis of a stereoisomer of frullanolide utilizing the intramolecular cyclization of co-formyl-2-alkenylsilane. Bull. Chem. Soc.. Jpn., 66, 2298, 1993. Kuroda, C., Inoue, S., Kato, S., and Satoh, J.Y, Synthesis of a-methylene-y-lactones fused to a perhydro azulene carbon framework through intramolecular cyclization of allylsilanes, 7. Chem. Res. (M), 458, 1993. 

Formyl-azulen86 Zu 0,117 g Azulen in 10 m/Triethoxymethan gibt man bei 7-8°eine Mischungaus 0,25 ml Perchlorsaure und 10m/Triethoxymethan. 1 -Ethoxymcthylen-azuleniumperchlorat (Schmp. 113-116°, Zers.) fallt aus. Man hydrolysiert mit kaltem, waBr. Aceton (1 1) Ausbeute 0,119 g (84%) (purpurfarbenes Ol). 

Aza-azuleno[2,l-b] thiophen has been prepared from 2-chloro-3-formyl-l-aza-azulene by annelating the thiophen ring by the Fiesselmann reaction. ... 

Electrophilic aromatic substitution reactions of compounds 10 occur in a fashion characteristic for heterocyclic analogues of azulene, and are specific at positions 5 and 7 <1994CB1479>. Thus, 10a (R = H, R = Ph) was successfully brominated, formylated, and acylated, as shown in Scheme 7. 

Azulene (112) is easily formylated in the 1- (or 1- and 3-) position(s). Decarbony-lation of such azulene intermediates has now been reported under mild conditions reaction with pyrroles in acetic acid at ambient temperature. Thus formylation of azulene is now a feasible strategy for protection of its five-membered ring. 

Formylation of Aromatic Rings. The Vilsmeier reagent attacks electron-rich aromatic systems to form aryl-methyleneiminium ions which liberate a formylated aromatic compound upon hydrolysis (eq 2). Thio- and selenoaldehydes can be prepared by hydrolysis in the presence of Sodium Hydrogen Sulfide or Sodium Hydrogen Selenide. A wide range of aromatic systems can be formylated in this fashion, including benzene derivatives, polyaromatic hydrocarbons (eq 3), and azulene. Substitution occurs at relatively electron-rich positions. 

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