Reaction with azulene

The mechanism of this reaction has not been as yet completely established. Obviously, metal alkyls formed initially, are decomposed (by illumination) to coordinatively unsaturated species (possibly via metal hydride intermediates), which then form the olefin complexes. The known 53 ) Ni(1.5-cyclooctadiene)2 is obtained from NiCl2, i-CsH7MgBr and 1.5-cyclooctadiene 336>. The corresponding reaction with azulene and FeClg yields Fe(azulene)2 163) ... 

Thomas and Long488 also measured the rate coefficients for detritiation of [l-3H]-cycl[3,2,2]azine in acetic acid and in water and since the rates relative to detritiation of azulene were similar in each case, a Bronsted correlation must similarly hold. The activation energy for the reaction with hydronium ion (dilute aqueous hydrochloric acid, = 0.1) was determined as 16.5 with AS = —11.3 (from second-order rate coefficients (102At2) of 0.66, 1.81, 4.80, and 11.8 at 5.02, 14.98, 24.97, and 34.76 °C, respectively). This is very close to the values of 16.0 and —10.1 obtained for detritiation of azulene under the same condition499 (below) and suggests the same reaction mechanism, general acid catalysis, for each. 

The mechanism for this photoreaction has not been elucidated, although it has been ascertained that these products are not observed in the dark reaction with acetone under the same conditions as used in the photolysis. The source of the isopropylidene unit is undetermined, but since all extraneous organic sources were excluded in the experiment, it seems clear that it originates from the azulene system itself, presumably from the five-membered ring. 

The reaction with disubstituted formamides and phosphorus oxychloride, called the Vilsmeier or the Vilsmeier-Haack reaction,is the most common method for the formylation of aromatic rings. However, it is applicable only to active substrates, such as amines and phenols. An intramolecular version is also known.Aromatic hydrocarbons and heterocycles can also be formylated, but only if they are much more active than benzene (e.g., azulenes, ferrocenes). Though A-phenyl-A-methyl-formamide is a common reagent, other arylalkyl amides and dialkyl amides are also used. Phosgene (COCI2) has been used in place of POCI3. The reaction has also been carried out with other amides to give ketones (actually an example of 11-14),... 

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. 

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 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... 

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. ... 

Arylbenzotriazoles (797) are prepared via 2-nitro- and 2-amino-diphenylamines (Scheme 161). The 2-nitrodiphenylamines (796) are prepared from the appropriate aniline by reaction with 2-fluoronitrobenzene in the presence of KF <808215,85JCS(Pl)2725>. Azo-coupling of 2-amino-1-cyano-azulene (798) with p-tolyldiazonium chloride gives (799) (Scheme 162). Catalytic reduction of (799) quantitatively yields the diamino derivative (800), which on diazotization affords 9-cyano-azuleno[l,2-J]triazole (801) in 77% yield <85TL335>. 

Photoreduction was quenched by high concentrations of biacetyl, slightly retarded by iodonaphthalene, but not affected by azulene or anthracene.113 These observations led to the unsatisfying conclusion that reduction proceeded via a triplet state which could be only selectively quenched. However, later work114 using flash photolysis showed that the benzophenone ketyl radical was generated upon irradiation of solutions of benzophenone and acridine, and that its predominant mode of disappearance was by reaction with... 

In the reactions of azulene with trimethylsilylruthenium carbonyl complexes in refluxing heptane, there occurs a migration of organosili-con groups from metal to ligand to give complexes of silylated azulenes (94) ... 

In the reaction of azulene with [Ru(CO)4SiMe3]2, two other products were isolated, namely Ru2(CO)2(C1oHg) (10% yield) and Ru2(SiMe3)2 (CO)4(C10Hg) (5% yield). The probable structure of the diruthenium compound 94) is... 

Wittig reactions with pyrrole-2-aldehyde led to the esters (79) which were cyclisized to 3a-azaazulen-4-ones (80).104,105 4-Methylene-3a-aza-azulenes (81) have been obtained from 80 with stabilized phos-phoranes.36 Reaction of dimethyl acetylenedicarboxylate with 81 could not be achieved. A similar cycloaddition was successful in the synthesis of cycl[3,3,3]azines (2) (Section V). 

Decomposition of l-diazo-4-arylbutan-2-ones offers a direct entry to bicyclo[5.3.0]decatrienones and the approach has been extensively used by Scott and coworkers to synthesize substituted azulenes.137 Respectable yields were obtained with copper catalysis,137 but a more recent study24 showed that rho-dium(ll) acetate was much more effective, generating bicyclo[5.3.0]decatrienones (154) under mild conditions in excess of 90% yield (Scheme 34). The cycloheptatrienes (154) were acid labile and on treatment with TFA rearranged cleanly to 2-tetralones (155), presumably via norcaradiene intermediates (156). Substituents on the aromatic ring exerted considerable effect on the course of the reaction. With m-methoxy-substituted systems the 2-tetralone was directly formed. Thus, it appeared that rearrangement of (156) to (154) was kinetically favored, but under acidic conditions or with appropriate functionality, equilibration to the 2-tetralone (155) occurred. 

The condensation reaction gives very high yields, but the preparation of the reactants (106) is often complicated. For the preparation of pseudoazulene systems 5 and 6 formed by exchange of two C—C bonds of the seven-membered ring in azulene (Scheme 1), five-membered dicarbonyl compounds of type 107 are used. Their reaction with alkyl or aryl hydrazines gives heterocyclic bases (108), which can be transformed to the pseudoazulene system (49) by alkylation and deprotonation (see Section III,A,l).136... 

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... 

Photo-induced H-abstraction of anthraquinone from xanthene has been studied using nuclear polarization-detected EPR and the structure of the resulting short-lived radical pair determined.194 The retrodisproportionation reactions of a variety of styrenes with 9,10-diliydroanthracene (DHA), xanthene (XAN), and 9,10-dihydroacridine (DHAc) have been studied in order to determine if there was any evidence of the alternative hydride-transfer mechanism in competition with the proposed H-atom-transfer mechanism. No such evidence was found.195 The reaction between azulene and DHAC... 

The carbodiimide 73, obtained by reaction of an iminophosphorane with ethyl isocyanate, underwent a thermally induced cyclization in 1,2-dichlorobenzene at reflux to give the azulene 74 in 42% isolated yield (Scheme 33) <2001JOC6576>. This process was regiospecific since products arising from reaction with the six-membered ring were not observed. 

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... 

Reactions with I3 on alumina. A mixture of an arene and iodine when shaken with alumina previously dehydrated at 400° can undergo iodination at temperatures above 110°. The method is useful for reactive arenes. Thus azulene can be converted to the 1,3-diiodo derivative in quantitative yield. 

---