Azulenyl synthesis

We have reported the synthesis of a series of azulene-substituted methyl cations, i.e., tri(l-azulenyl)methyl, di(l-azulenyl)phenylmethyl, and (1-azul-enyl)diphenylmethyl cations (2a+, 3a+, and 4a+) (Figure 6) (6). In order to examine substituent effects on the azulene rings and to enhance their stabilities, a series of the cations (2b-d+, 3b-d, and 4b-d+) bearing tert-buty groups on each azulene ring were also synthesized (7). 

The methoxy substituents on each azulenyl ring stabilized the carbocation effectively (12). The reaction of 6-methoxyazuiene (13) with 6-methoxyazulene-1-carbaldehyde (12) in acetic acid did not afford the condensation product 14, because of low reactivity of these compounds and lack of stability of product 14 under the reaction conditions. However, a high-pressure reaction (10 kbar) afforded the desired hydro derivative 14 in 6% yield. Synthesis of the cation 15+ was accomplished by hydride abstraction from the hydro derivative 14 (Figure 9). 

The tri(azulenyl)methane derivative 24+ including a 6-azulenyl group was prepared by the reaction of azulene 6b with diethyl 6-formylazulene-l,3-dicarboxylate. Synthesis of 24+ was accomplished by hydride abstraction with DDQ. Cation 24+ was isolated as a hexafluorophosphate salt by treatment with aqueous HPF6. The new salt is a stable, deep-green colored crystals, that can be... 

The synthesis and characterization of a series of azulenyl-substituted cations (223) showed468,469 that these are extremely stable ions, which is attributed to the dipolar structure of the azulene rings. 

The stable did -azulcnyl)thieno[3,2-9]thiophene-2,5-diyl spacers 78a and 78b were prepared by hydride abstraction of the corresponding 2,5-bis[bis(methyl and 3,6-di-tert-butyl-l-azulenyl)methyl]thieno[3,2-9]thiophenes 77a and 77b, the synthesis of which was established by the reaction of 1-methyl- and 1,6-di-t-butylazulcncs 75a and 75b with thicno 3,2-9 thiophene-2,5-dicarbaldehyde 76 (Scheme 11). The dications 76 showed high stability with large pA"R+ values. The electrochemical behavior of 78 was examined by cyclic voltammetry (CV). Chemical reduction of 78 with Zn powder in acetonitrile afforded 79 as deep-colored crystals, which exhibited rather high... 

The azulenyl furanone 60 was a key intermediate in the synthesis of the monofunctional azulenyl squaraine dye NIRQ700 61 (NIRQ = near-infrared quencher) <2003TL3975>. The resulting nonfluorescent squaraine dye absorbed in the 600-700 nm range and can potentially be used to quench a number of available NIR fluorochromes in order to extend the spectrum of biological quenching assays. 

Crombie, A.L., Kane, J.L., Shea, K.M. and Danheiser, R.L. (2004) Ring expansion-annulation strategy for the synthesis of substituted azulenes and oligoazulenes. 2. Synthesis of azulenyl halides, sulfonates, and azulenylmetal compounds and their application in transition-metal-mediated coupling reactions. J. Org. Chem., 69, 8652-67. 

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