Rearrangement azulene-naphthalene

Skeletal rearrangements of cycloalkanes containing 9-18 carbon atoms were observed for the first time by Prelog et al. (162) on Pd/C catalysts at 400°C. Under these conditions, polycyclic aromatic and pseudoaromatic hydrocarbons are obtained (indene, azulene, naphthalene, phenanthrene, etc.). By carrying out the reaction on Pt/C under less drastic conditions, Kazanskii et al. (163) could observe the precursors of the aromatics as primary products. The latter are bicycloalkanes resulting from transannular 1-5 or 1-6 dehydrocyclizations (Scheme 84). For instance, cyclooctane yields... 

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... 

The rearrangement of azulene to naphthalene induced by excitation into the S2 state has been examined under collision free conditions in a molecular beam and an approximate estimate of the rate constant for the rearrangement under these conditions has thereby been determined. ... 

Whereas bicyclic azulenes suffer thermal isomerization to )tield naphthalene derivatives (52CRV127, p. 169 85HOU(5/2c)127, p. 413), there are a few examples of transforming an azulene-fused heterocyclus to another heteroring or of rearranging it to benzene. The formation of azulenopyrrole 194 from azulenofuran 164 (61CIL1715) was mentioned previously (Section 2.4.1.6). 

Pericydic Processes involving Non-concerted Steps.—Synthesis of triquinacenes have been discussed above. The hydrocarbon (388) [=(359)] is remarkably stable to heat. At 600 °C it gives azulene in low conversion with loss of 2H. At 700 °C the azu-lene secondarily isomerizes to naphthalene but t,2-dihydronaphthalene is also formed from triquinacene. At 750 °C some indene is formed with loss of CH2. The formation of azulene is unexpected. It is suggested that initial loss of 2H takes the molecule out of the set of (CH) o isomers and skeletal rearrangement via (389) to azulene is a possibility. At the higher temperatures isomerization via (390)—(393) would provide a path to the other products, each step being known or reasonable. The rates of the thermal conversions (394) (395), (395) - (396X and (394) - (396) at 200 °C are... 

Acetic acid/irradiation Photoisomerization of isocyclics Azulene from naphthalene ring Santonin rearrangement... 

Early examples of application of this reactive CPMD approach were the chemical rearrangement of azulene into naphthalene [62], where new mechanisms and alternative possible pathways were evidenced for the first time, the synthetic organic reactions in supercritical water for the production of nylon synthetic fibers [63], and phase transitions in various materials from zeolites to graphene [64]. 

Skeletal rearrangement with decarboxylation Azulene from naphthalene ring... 

A close study of deuteriated azulenes showed that, in the mass spectrometer, 72% of ions suffer complete hydrogen scrambling prior to expulsion of —CH2—. The rearranged ions are the same as those in the spectrum of naphthalene. The reaction of sodium cyclopentadienide with pyrylium salts has been used to make several more azulenes, e.g. (24), and chlorination of 4,6,8-trimethylazulene in H2SO4 has been studied. ... 

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