Azulen

The generic term azulene was first applied to the blue oils obtained by distillation, oxidation, or acid-treatment of many essential oils. These blue colours are usually due to the presence of either guaiazulene or velivazulene. The parent hydrocarbon is synthesized by dehydrogenation of a cyclopentanocycloheptanol or the condensation of cyclopentadiene with glutacondialdehyde anil. 

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

Flassoon S, Oref I and Steel C 1988 Collisional aotivation of quadrioyolane by azulene an example of very strong oollisions J. Chem. Rhys. 89 1743-4... 

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],... 

Among other aromatic compounds that have been tricyanovinylated are phenanthrene (23), o-alkylphenols (24), pyrrole (23), indoles (23,25), 2-meth5lfuran (26), azulenes (26,27), diazocyclopentadiene (28), and a variety of phenyUiydrazones (26). 

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). 

Azulene, 4,b,8-trimethyl-from pyrylium salts, 3, 660 Azulenes... 

Azulene (2) A mixture of 2-isopropyl-4,7-climethylindane 1 (200 g, 1.91 mol) and ethyl diazoacetate (50 g, 0.5 mol] was heated for 1 h at 130°C. Vacuum distillation and recovery ol 1 (160 g) gave a brown residue which was heated with 40% NaOH (40 mL) and EtOH (200 mL). The unreacled ester was extracted with Et20 and the aqueous solution was acidified to obtain crude 2, which after distillation afforded 24 g ol 2(52%), bp t60-185°C/ 2mm. 

The blue pyridine distillate is redistilled through a 50-cm vacuum-jacketed Vigreux column (to avoid loss of azulene) until approximately 1.7 L is collected the residual azulene is combined with the main residues for extraction. 

Alumina was purchased from Macherey, Nagel and Co., Diiren (FRG). The checkers employed 650 g of neutral alumina (Fisher, adsorption grade, 80-200 mesh) packed in a 40-cm high column. Yellow impurities remained on the column, while the blue azulene came off with the hexane solvent front. 

Further purification of azulene may be achieved by sublimation at reduced pressure, mp 99 C. The checkers found that mechanical losses, particularly as mentioned in Note 9, lead to reduction in yield with reduction in scale (0.1 mol, 39% yield 0.5 mol, 43% yield 0.8 mol, 79% yield). 

Substituted azulenes can be prepared in the same manner by the use of substituted cyclopentadienes or substituted pentamethinium salts. 

Azulene does have an appreciable dipole moment (0.8 The essentially single-bond nature of the shared bond indicates, however, that the conjugation is principally around the periphery of the molecule. Several MO calculations have been applied to azulene. At the MNDO and STO-3G levels, structures with considerable bond alternation are found as the minimum-energy structures. Calculations which include electron correlation effects give a delocalized n system as the minimum-energy structure. ... 

In contrast to the significant resonance stabilization of azulene, pentalene and heptalene are indicated to be destabilized relative to a reference polyene ... 

Polycyclic aromatic hydrocarbons, naphthylamines After application of the sample solution place the TLC plate in a darkened iodine vapor chamber (azulene a few minutes, PAH several hours). Then remove the excess iodine at 60 °C. [20]... 

The condensation of a vinylogous formamide with an enamine has been applied to an aza azulene synthesis (351). The point of attachment of the aldehyde to the enamine in condensations with indolenin derived poly-enamines was found to favor the second double bond (352,353). 

Examine electrostatic potential maps for naphthalene, azulene and hexaphenyltriafulvene. 

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