Azulenes hydro

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-... 

The dication 212+ composed of two methylium units connected to a p-phenylene spacer would be a candidate for new Wurster type violene-cyanine hybrid (Figure 12) (15). The reaction of four molar amounts of azulene 6b with terephthalaldehyde yielded the hydro precursor. Synthesis of the dication 212+ was accomplished by hydride abstraction with DDQ in almost quantitative yield. The dication 212+ was expected to show destabilization, but instead it exhibited high thermodynamic stability just like the corresponding monocation 3b+. 

As appropriate model compounds for these reactions240 the bridgehead substituted di hydro-4-methyleneazulenes 474 were employed. Allyl-, crotyl- and propargyl-substituted dihydroazulenes 474 and 476 can be easily rearranged to the 4-substituted azulenes 475 and 477 (equations 179 and 180) whereas all attempts to obtain 4-benzylazulene 479 by rearrangement of precursor 478 gave only polymeric products (equation 181). Undoubtedly, this failure can be explained by the fact that the Cope rearrangement becomes very... 

Giguere, R.J., Duncan, S.M., Bean, J.M., and Purvis. L.. Intramolecular [3 + 4] allyl cation cycloaddition. Novel route to hydro azulenes. Tetrahedron Lett.. 29. 6071. 1988. 

Olefin cyclization (3, 305-307 4, 531-532 5, 696-697). A key step in a novel synthesis of ( )-longifolene (6) from (1) involves the acid-catalyzed cycUza-tion of (2) to (3) with TFA at 0°. The original paper suggests a mechanism for the cychzation of (2) mainly to the bicyclic product (3) rather than to a hydro-azulene derivative. ... 

Azomethinium ylids, N-metalated -, syntheses with - 43, 904 Azonia-Cope rearrangement-Mannich cyclization 41, 938, 982 lif-Azonine ring, 2,3,4,5,8,9-hexa-hydro-, 5-aryl-, N-protected 44, 579 Azoxy compds. 44, 18 Azulen-2-ones, hydro- 43, 640 Azulen-4-ones, perhydro-l-methylene-43, 955... 

The approach to cycloheptadienes via thermal Cope rearrangement of an appropriate 1,2-divinylcyclopropane is an attractive one, limited only by the availability of the latter. A number of groups of workers have now described efficient routes to divinylcyclopropanes based on addition of 2-vinylcyclopropyl-lithium or -cuprates to 3-alkoxy- or 3-halogeno-cycloalk-2-enones (Scheme 30), and extensions of these studies to the total synthesis of the biologically important natural hydro-azulene systems are anticipated. 

Applying a different intramolecular cyclization strategy, Posner and his coworkers have demonstrated that direct -addition of a methyl metal reagent to the or,jS-unsaturated cyclopentenone (197) results in ring closure to the hydro-azulene system (198). The procedure can be carried out more effectively by trapping the intermediate enolate as a trimethylsilyl enol ether (199) before cyclizing, by treatment with titanium tetrachloride (Scheme 24). 

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