Azulenes salts

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

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

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. ... 

When azulene is heated with sulphuric acid and acetic anhydride a sulphonic acid, soluble in water, is formed. This acid forms a fine violet sodium salt. This sodium salt is not very stable when kept for three months it decomposes into a mixture of oil and resin. Its aqueous solution gives blue precipitates with calcium and barium salts. 

Besides the carbocations mentioned above, numerous highly stable carboca-tions have been isolated as the salts of inorganic anions. Azulene analogues of triphenylmethylium ion [ll ]-[20 ], [21 j, [22 " ] and [23 j trisubsti-tuted cyclopropenylium ions [l" ] and [24 ]-p6 ] cyclopropyl-substituted tropylium ions [27 ]-[30 ] tropylium ions annelated with bicyclic frameworks [31 ]-[36 ] and [37 ]-[39 ] fulvene-substituted cyclopropenylium [40 ] and tropylium [41 ] ions a tropylium ion condensed with acenaphthylene [42 ] and a cation containing a 147t periphery [43 ] have... 

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. 

Trimethylpyrylium perchlorate is a very versatile and useful starting material. Thus its reaction with cyclopentadienyl-sodium has made 4,6,8-trimethylazulene 12 easily available for general studies of the properties of azulenes 18 and for the synthesis of related compounds.14 In addition, pyrylium salts are readily converted to a variety of pyridine derivatives 9 15 as well as to derivatives of nitrobenzene16 and phenol.9 17,18 It is clear that its value as a starting material is such that it is receiving wide use. 

The reaction of salt 369 with acetic anhydride affords a cyclized product characterized as 2-methyl-1,3,3a,9-tetra-zacyclopentant[ ]azulene 370 (Scheme 38) <1999J(P1)1339>. The reaction of l,2-diamino-l,3-diazaazulenium compound 369 with diethyl ethoxymethylenedicarboxylate (DEEM) provides a complex reaction mixture, one of the isolated products being compound 21, which is isolated in 29% yield when the reaction is carried out in ethanol, but in 47% yield, when acetonitrile is used as solvent (Scheme 38) <1999J(P1)1339>. 

Finally, the pyrrolo[2,l-/ [l,2,4]triazine moiety was also encountered in azulene derivatives. Reactions of l,8-diamino-3-phenyl-l-azaazulenium salt 54 with triethyl orthoformate and acetic anhydride gave l-phenyl-2a,3,5-mjzjbenzb. //]jzulcncs 55 and 56. The reaction of the same salt with ethyl pymvate gave 4-acetyl-l-phenyl-2a,3,5-triazabenz[c, /]azulene 14 <2000H(53)323>. 

Figure 7. Preparation of the azulene-substituted methyl cation salts 2a-it PFf ...

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 allenylsilanes are excellent nucleophiles and they can react with a variety of electrophilic species in annulation processes that provide access to diverse products. Allenylsilane 112 (Eq. 13.36) reacts with tropylium fluoroborate 111 to provide azu-lene 113 [35]. The reaction is slow and it is necessary to use an acid scavenger so as to inhibit protiodesilylation by the fluoroboric acid that is generated during the course of the annulation. The excess tropylium salt abstracts a hydride from the reaction intermediate leading to the azulene. There are relatively few direct methods for the synthesis of azulenes. 

Triphenylpyrylium tetrafluoroborate is a versatile and useful stable starting material. Its reaction with nitromethane under basic conditions has made 2,4,6-triphenylnitrobenzene easily available. In addition, pyrylium salts are readily converted to a variety of pyridine derivatives i i . 20 including alkyl- and arylpyridinium salts, to thiopyrylium salts," and to substituted azulenes. ... 

Azo coupling of diazonium salts with aromatic (or pseudoaromatic) hydrocarbons is possible if the coupling agent is highly substituted. For example, azo compounds have been produced from pentamethylbenzene [12], benzpyrene [13], and azulene [1-4]. 

Hafner s synthesis of azulene,216 the cyclopentadienyl anion can also be used to introduce the five-membered fragment. This anion reacts with heterocyclic quaternary salts in a complex manner the pseudoazulene, however, is obtained in one step. The total yields are only about 10%, but it is possible to use starting materials that are easily available in large quantities. This variant was applied to prepare 2H-cyclopenta[thiadiazolium salts145 and cyclopenta[c]thiopyranes (31) using N-methyl thiazoliumbromide.90... 

Protonation represents the simplest electrophilic reaction. Contrary to azulene (pKa = — 1.7)237 most pseudoazulene systems are relatively strong bases. The pK.d values are listed in Table V. Numerous pseudoazulenes can be obtained from their quaternary salts by the action of sodium acetate (see... 

Only a few investigations of electrophilic substitution reactions of pseudo-azulenes containing a pyrrole-type nitrogen have been reported. There are many examples of alkylations (see Table VI). An alkylation always takes place at the nitrogen of the five-membered ring. For 7H-pyrrolo[2,3-b]-pyridine 68 azocoupling and reaction with dithiolium salts have been reported.166... 

OB to C02 —118.6% colorl crysts from hot w mp 245—47° with decompn CA Registry No [940-93-2]. It is prepd by the reaction between tert-Bu ale, Ac20, and perchloric ac or between 4-me-3-butene-2-one, Ac20, and perchloric ac (Ref 2). Caution The salt is expl and the prepn should be carried out behind a good shield. Its impact sensy is similar to RDX. The dry crysts are especially sensitive and they should not be crushed, rubbed, or pushed thru a narrow opening. The compd is a useful reagent for the prepn of azulenes, pyridines, and other... 

Of particular interest is the observation that in certain cases products such as 24 resulting from domino processes are obtained After the formation of the furan, evidently a double Michael-type addition of these intermediates to the remaining starting material 23 can take place at the unsubstituted 5-position. Preliminary experiments to investigate scope and limitations of such addition reactions in the presence of gold salts also confirm the applicability to the functionalization of other electron-rich arenes (Scheme 6) Besides furans, azulene 28 and di- and trialkoxybenzene are suitable as nucleophiles for the reaction with unsaturated carbonyl compounds [14]. For instance, 2-methylfuran (25) reacts at the reactive 5-position with methyl vinyl ketone 26 to give the addition product 27, and with azulene 28 a twofold... 

Among 6-alkyl and 6-aryl derivatives of salts 228a,b, the location of the maximum (Amax = 652-720 nm) exhibits little dependence on the nature of the heteroatom (2-position) or the substituent at C-6 (68ZOR907 69ZOR961), but rather is determined by the azulene moiety—i.e., by the electronic contribution of heteronium structures like 341b (see Scheme 88). 

The reactivity of these methyl groups is normally enhanced by nitrogen atom quaternization. Benzotroponopyridinium salt 505 with two molecules of azulene aldehyde condenses to afford blue-black bis(azulenylvinyl) dye 506 (Amax 536 nm 62ZC369). Furthermore, oxazolium salt 507 condenses with activated benzothiazolium salt 508 (Scheme 134) to form unsymmetri-cal trimethine cyanine 509 (63UP1). (Dyes 512a,b arise from methylthio exchange Section IV,A,5,e.)... 

In some cases, like reduction of azulene or for anodic waves, corresponding to mercury salt formations with various ligands, two or even three consecutive adsorption waves can be observed at gradually increased concentration. Two or three adsorbed layers can be formed, which can differ in chemical composition, in number and structure of adsorbed layers, or in orientation of compounds in such layers. 

Perchlorate salts are used as electrolytes in - electropolymerization reactions involving monomers such as aniline, benzidine, azulene, biphenyl, di-vinylbenzene, and indole. 

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