Azulenes reactions

Synthesis of Azulenes. Reaction of tropylium cations with allenylsilanes produces substituted azulenes. Typically, commercially available tropylium tetrafluoroborate (2 equiv) is ert5)loyed. The second equivalent dehydrogenates the dihydroazu-lene intermediate to produce the aromatic product. Poly(4-vinyl-P3Tidine) (poly (4-VP)) or methyltrimethoxysilane is used to scavenge the HBF4 produced in the reaction. 

Azulene is an aromatic compound and undergoes substitution reactions in the 1-position. At 270 C it is transformed into naphthalene. 

The cyclic 2,4-dienoate 184, formed by the Pd-catalyzed cyclization of the 1,6-enyne 183, reacted with 154 to form the azulene derivative 185[118], The 3-methylenepyrrolidine 188 is formed by the reaction of the Zn reagent 186 with the chiral imine 187 with high diastereomeric excess. The structure of the allylic ethers is important for obtaining high diastereoselectivity[l 19],... 

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

During the 1950s and 1960s Hafner used Konig salts, derived from the reaction of A -methyl aniline with Zincke salt 1, for azulene synthesis. The Zincke reaction also achieved prominence in cyanine dye synthesis and as an analytical method for nicotinamide determination. ... 

Unlike azulene, 3-phenylcyclopent[e]azepine (1) undergoes cycloaddition with diphenylacetyl-ene to give cycloadduct 2 which, under the reaction conditions, eliminates benzonitrile to give... 

SECOND-ORDER RATE COEFFICIENTS FOR REACTION OF [1-3H]-AZULENE (A) AND... 

Thomas and Long488 also measured the rate coefficients for detritiation of [l-3H]-cycl[3,2,2]azine in acetic acid and in water and since the rates relative to detritiation of azulene were similar in each case, a Bronsted correlation must similarly hold. The activation energy for the reaction with hydronium ion (dilute aqueous hydrochloric acid, = 0.1) was determined as 16.5 with AS = —11.3 (from second-order rate coefficients (102At2) of 0.66, 1.81, 4.80, and 11.8 at 5.02, 14.98, 24.97, and 34.76 °C, respectively). This is very close to the values of 16.0 and —10.1 obtained for detritiation of azulene under the same condition499 (below) and suggests the same reaction mechanism, general acid catalysis, for each. 

Azulyl sulphoxides 127 have also been prepared by a reaction involving a direct electrophilic substitution on the azulene ring by alkane- or arenesulphinyl chlorides186 (equation 69). Preparation of the methyl and phenyl sulphoxides of 4,6,8-tri-methylazulene and 4,6,8-tri-isopropylazulene by this method resulted in fair yields (57— 72%). However, the substitution on azulene itself gave only low yields of the corresponding sulphoxides. 

Azulene quinones [49b] are compounds related to the family of tropones and are considered to possess great biological and physiological potential. Several polycyclic compounds have been prepared by high pressure (3kbar, PhCl, 130°C, 15h) Diels-Alder reaction of 3-bromo-l,5-azulene quinone (137) and 3-bromo-l,7-azulene quinone (138) with several dienophiles. The cycloadditions were regioselective and afforded cycloadducts in reasonable to good yields (Scheme 5.20). 

The mechanism for this photoreaction has not been elucidated, although it has been ascertained that these products are not observed in the dark reaction with acetone under the same conditions as used in the photolysis. The source of the isopropylidene unit is undetermined, but since all extraneous organic sources were excluded in the experiment, it seems clear that it originates from the azulene system itself, presumably from the five-membered ring. 

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. 

C-TMS protection of the alkyne provided acceptable yields of 3-substituted indole as long as the hydroxy group was protected with a stable group. Purple colored impurities, one of which has been identified as azulene 45, were seen in both coupling reactions using C-TMS-alkynes such as 36 and 40d (Scheme 4.9). The azulene was presumably formed through the dimerization of acetylenes... 

The observations that the pss depends upon the sensitizer concentration (for low-energy sensitizers Et < S3 kcal/mole) and that added azulene (Ef = 30 kcal/mole) alters the [Cy [T], ratio so that the pss contains more fra/w-stilbene requires the addition of the following reactions ... 

These reactions, while not very important for high-energy donors in the absence of azulene, do help define what the potential energy diagrams should look like, that is, the fram-stilbene triplet is a discrete intermediate while the cij-stilbene triplet is a high vibrational form of the phantom triplet. Herkstroeter and McClure(13> have been able to observe the fro/w-stilbene triplet via flash photolysis using low-temperature glasses however, no similar triplet was observed for cfr-stilbene. Only when they studied cfr-stilbene-like... 

In addition,<1,48,48) it was noted that whereas the azulene effect on the sensitized reaction is sensitive to changes in solvent viscosity, the azulene effect on the direct photoreaction was independent of solvent viscosity, as would be predicted for Forster-type energy transfer. The inescapable conclusion is that cis-trans isomerization upon direct irradiation of stilbene takes place in the singlet manifold. 

On adding one drop of nitrobenzene to an equimolar, ten millimolar, mixture of the other two solids a violent reaction produced gas and carbonaceous material. This was initially attributed to the oxidative powers of the nitrobenzene [1], However, diphenylacetylene is a high energy molecule, AH°f +315 kJ/mole. At least 98% of the potential chemical energy present will have been the diphenylacetylene. It is probable that the nitrobenzene merely provided a liquid phase in which the aluminium chloride could interact with the acetylene, catalysing reaction beyond the intended azulene dimerisation product[2]. 

Stirling, A. Iannuzzi, M. Laio, A. Parrinello, M., Azulene-to-naphthalene rearrangement the Car-Parrinello metadynamics method explores various reaction mechanisms, Eur. J. Chem. Phys. Phys. Chem. 2004, 5, 1558-1568... 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

Nagashima reported the hydrogenation of di-, tri- and tetranuclear ruthenium complexes bearing azulenes below 100 °C revealed that only the triruthenium compounds reacted with H2 via triruthenium dihydride intermediates.398 This indicates that there exists a reaction pathway to achieve facile activation of dihydrogen on the face of a triruthenium carbonyl moiety.399... 

Asymptotic analysis, electronic states, triatomic quantum reaction dynamics, 317—318 Azulene molecule, direct molecular dynamics, complete active space self-consistent field (CASSCF) technique, 408-410... 

Photolysis of the triazepine products produces 2,2-dimethylpropanenitrile and the corresponding pyrazole in quantitative yield <1997BSF927>. Reaction of sydnone 89 with fulvene 91 proceeds by [ji4s + jt6s]-cycloaddition followed by spontaneous loss of carbon dioxide and a molecule of dimethylamine or acetic acid from the pseudo-azulene , cyclopentaMpyridazine 92 (Equation 9) <1996CC1011, 1997T9921>. 

The 14 re-electron [S Ns]"1" cation is formed by the reaction of S4N4 with the [SN]+ cation.42 The planar, 10-membered ring usually has an azulene shape (19), with alternating sulfur and nitrogen atoms. Electrochemical reduction of S5N5+ salts in acetonitrile produces the polymer (SN)X. 

The predicted conrotatory cyclization of octatetraenes was confirmed for the case of the methyl-substituted compounds, which above 16 °C readily formed the cyclooctatrienes shown in equations 13 and 14)14. We conclude this section with an electrocyclic reaction involving ten TT-electrons, that is, the formation of azulene (17) when the fulvene 16 is heated (equation 15)15,16. 

Compound R Conditions of reaction Yields (%) (related to the turnover of the azulene) 28 29 Reference... 

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