Arylation azulenes

The arylation of electron-rich arenes, such as azulene (55)206 and heteroarenes, has been sporadically described. Under similar conditions phenols undergo arylation, which is preferably directed at the ort/zo-positions, probably due to the involvement of palladium phenolate intermediates.188,207 Polysubstitution occurs readily.208 The para-position can be attacked only with the sterically hindered 2,6-di-t-butylphenol.209 Similar ortho-diarylation of arenes bearing carbonyl groups (acetophenone, anthrone, benzanilide, etc.) shows that the or//zo-di reeling effect of the substituent is more important than its other electronic effects.189... 

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... 

Lithium alkyls or aryls add to pseudoazulenes 3398100 and 39.113-114 The carbanion always reacts with the carbon atom opposite the heteroatom in the six-membered ring (Scheme 16). After hydrolysis of primary intermediate 121 dihydro products (122) are formed, which can be transformed to pseudoazulenes in the usual manner (see Section III,A,2). The structure of primary intermediate 121 is confirmed by its alkylated (or acylated) products (123). Even these compounds can easily be dehydrogenated to pseudo-azulene. In this way. substituted pseudoazulenes can be formed that are not obtainable otherwise. The direction of addition to the pseudoazulenes is the same as in azulenes.241... 

This mechanistic consideration is in accord with the result from arylation of indene (7) [5]. The arylation occurs exclusively at the 1,3-positions, those with the highest electron density, of intermediary indenyl anions (9). The related arylation of azulene also proceeds exclusively at 1,3-positions, interpreted as electrophilic aromatic substitution, again by an electrophilic aryl-Pd species [10]. 

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 reaction of arenes with aryllead tricarboxylates performed in trifluoroacetic acid, affording biarenes, takes place via a cationic 7t-complex.162 Since azulenes form 7r-donor/acceptor complexes with various 7r-acids, the arylation of 4,6,8-trimethylazulene 108 was attempted with />-methoxyphenyllead triacetate 1 (Equation (135)).163 Only one isomer of 1-arylazulene 109 was formed although in a modest 27% isolated yield. Based on recovered unreacted azulene, the effective yield was 43%. A dimer 110, 3,3 -dianisyl-l,l -biazulene (4% yield), was suggested to result from the one-electron oxidation of the intermediate 4-methoxyphenyl cation in the 7t-complex. 

In agreement with predictions based on frontier orbital arguments56, dienamines undergo [6 + 4] cycloaddition to alkyl or aryl fulvenes to give dihydroazulenes 66 and hence azulenes 67 and 68 in moderate yield57,58 (Scheme 35). 

Xu et al. [44] reported the microwave assisted synthesis and antifungal activity of 2,5-disubstituted-l,3,4-oxadiazoles containing azulene moiety. The 5-aryl-2-(3-methylazulen-l-yl)-l,3,4-oxadiazoles (Lv) were obtained by the microwave... 

Tellurocyanate ion reacts with benzyl halides aryl iodides , arenediazonium tetraflu-oroborates, and with azulene" to form aryl tellurium cyanides. 

Among the few known methods for catalytic direct arylations of simple arenes with aryl halides, early examples are represented by direct arylations of azulene (Scheme 9.29) [67] and of benzene [68]. 

Scheme 9.29 Palladium-catalyzed direct arylation of azulene (85).

Introduction of one or two phenyl groups in a-position shifts AT to the red (and prolongs tt) [299], Two transients with different AT and rT for 2-StN were attributed to two conformers [410,421], as already indicated by the effect of azulene on the sensitized photoequilibrium [422]. Detailed studies of the triplet of 1-StN and its C1-, Br-, and N02-derivatives have been published [122,199], Differences in the T-T absorption spectra of 2,2 -DNE at low temperatures have been ascribed to changes in the rotameric composition [423], T-T absorption spectra of various ADBs are available [142, 143,145, 146, 235, 411], For example, from a comparison with 3,4-dihydrophenanthrene (iT = 430, 580nm) a transient of an ADB with aryl = 2-naphthyl (1T = 400, 430nm) has been attributed to the trans triplet state [33],... 

Aryl- and heteroarylacetonitriles give compounds of type 194 (Eq. 158). When the aryl group is 7r-excessive (azulene or heteroaryl) and vinamidinium... 

Aerial oxidation of this affords anthraquinone in 37% yield. Both 1-naphthyl and 2,4-dimethylbenzene sulphonates follow the same path but yield only traces of the corresponding quinone. In the last case, 2,4-dimethylbenzenesulphonate, the quinone is accompanied by 0.8% of 2,4-dimethylphenol. The second path involves loss of sulphur trioxide to yield aryl radicals which afford the products, the arene and/or the biaryl, shown in Scheme 17212,213. Other studies have shown that anthraquinone-1-sulphonic acid (256)214,215 and anthraquinone-2-sulphonate216 are also photochemically labile. A study of the photochemical reactivity of azulene sulphonic acids has also been reported217. Photochromism has been studied with respect to the stilbene derivative 257218. 

Anomalies in the Bischler-Napieralski reaction were later reported (95TL2795) when substituents in the 2-aryl group of the aromatic N-methylnaphthylformamide were of a 2-alkoxy-4,5-methylenedioxy nature (70), but not with the equivalent 2-alkoxy-4,5-dimethoxy pattern (69). The former cyclized to a 12-azonianaphth[1.2-fe]azulene derivative 73 as an additional product to 72, whereas the latter cyclized normally to the benzo-[cjphenanthridinium chloride 71 (Scheme 9). 

Vinyliminophosphoranes derived from 1,6-methanol[10]-annulenes react with isocyanates to give 1,6-methanol[10]-annulenopyridines. Bis(vinyliminophosphoranes) combine with isocyanates to provide azolofused l,3-diazepines. Differences on the periphery of the fused ring systems occur based on isocyanato (alkyl vs aryl) substituents. The thermal reaction of [(2-azulenyl)imino] phosphoranes on [(1-azaazulen-z-)imino]-phosphoranes with 2-bromotropone allow for the preparation of 6-aza- and 6,7-diazaazuleno[1,2-a]azulenes. °... 

The intermediate carbenes generated from ketones and TMSC-(Li)N2 have also been shown to undergo 1,5 0-Si and N-H insertion to produce 5-trimethylsilyl-2,3-dihydrofurans and 2-pyrrolines or 3-substituted indoles, respectively (eqs 61 and 62). Azulene 1-carboxylic esters may be generated in moderate yield by the reaction of TMSC(Li)N2 with alkyl 4-aryl-2-oxobutanoates, followed by oxidation with manganese dioxide. ... 

C17H22O3, Mr 306.36, cryst., mp. 158-160°C. Flowers of chamomile (Matricaria chamomilla, Astera-ceae) contain ca. 0.15% of proazulenes, especially M., which can be obtained by chloroform extraction. When extracts containing M. are heated, elimination of water and acetic acid occurs to furnish chamazulene-carboxylic acid which, as an a-aryl-carboxylic acid, easily undergoes decarboxylation to chamazulene (see azulenes). 

Azulenes undergo condensation reaations with aryl and heteroaryl aldehydes in the presence of mineral acids to give azulenium salts, which can react with nucleophiles to give a variety of 1-substituted derivatives, e.g. [82,125,128,129]. 

The Ullmann reaction was used in the coupling of a wide variety of aryl halides, Ar-X, where the Ar includes mono-, di-, poly-substituted phenyl [4,5,14], naphthalene [4,5,15,16], azulene [17], pyridine [18], pyrimidine [19], thiophene [4,5,20], carbazole [21], and even ferrocene [22], while X = I, Br, Cl. The reaction was successfully used in the intramolecular cyclization reactions affording four- [23], five- [24], six-membered [25], and some other larger rings [6]. Selected examples where halides 10-13 were converted to biaryls 14-17 are given in the Scheme 2 [14,16,17,19]. 

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