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The lead(IV) oxide oxidation of various azulen-2-ol derivatives in acetic acid generates azulenoxy radicals via one-electron oxidation. The intermediates end up yielding recombined dimers, [1,1′-biazulene]-2,2′(1H,1′H)-dimers, as common type of products. In addition to these, hexacyclic cage dimers were obtained from 5-substituted azulen-2-ol derivatives. From dimethyl 2-hydroxyazulene-1,3-dicarboxylate, a hydroxyazulene having no substituent on the seven-membered ring was isolated a pair of dimethyl 2-hydroxy-4-[1,3-di(methoxycarbonyl)-2-oxo-1,2-dihydroazulenyl]azulene-1,3-dicarboxylate, but neither a cage dimer nor a 1,6-coupled dimer. The full structures of the dimers have been firmly established by an extensive X-ray crystallographic analysis and 13C NMR spectral comparisons of the key derivatives. Concerning the mechanism of the formation of the cage dimers, a [5+5] π cycloaddition followed by recombination of the resultant biallyl system is suggested.

Azulenequinones gave dimers when they were irradiated with a high-pressure mercury lamp. In polar solvents, head-to-head dimers were predominant, whereas head-to-tail dimers increased in less polar solvents. From 3-methoxy-1,5-azulenequinone, four products were obtained, while bromoazulenequinones and 1,5-azulenequinone gave a single dimer. The product distribution was dependent on the polarity of solvents, substituents, and concentrations.

Single-strand cleavage of DNA in a phosphate buffer at pH 6.0 was accomplished by photolysis of various 1,5- and 1,7-azulenequinones with 350-nm UV light; results from the analysis of a 32 P-end-labeled DNA fragment obtained by gel electrophoresis indicate the predominant cleavage occurring at the guanine residue.

Oxidation of 1-ethyl-, 1-propylazulenes, and their 5-isopropyl derivatives with bromine gave 3-bromo-1,5- and 3-bromo-l,7-azulenequinones (Type A) together with 3-bromo-l-hydroxy-5-isopropyl-l-alkylazulen-7-one and its isomeric products (Type B), while the same reaction of 1-methylazulenes afforded Type B products along with many unidentified products. On the other hand, 1-phenylazulene gave 3-phenyl-1,5- and 3-phenyl-l,7-azulenequinones (Type C) and Type B products in high yie]ds. 1,2-Polymethyleneazulenes afforded a considerable amount of 3-bromo-2-(ω-formylalkyl)azulenequinones together with Type B products. Possible pathways for the extrusion of the alkyl substituent at C-l are discussed.

The electronic structures of azulene (1) and its alkylated derivatives were investigated on the basis of MO calculations by MNDO and PM3 method. There results were experimentally evaluated by measu...

Azulenequinones have been attracting great interest in recent years. After a brief introduction concerning an earlier study of azulenequinones we review recently developed areas of azulenequinone chemistry, which became possible by the discovery of a facile one-pot synthesis of azulenequinones, or their bromo derivatives, by means of the bromine oxidation of various azulene derivatives in an aqueous solvent. Various functionalized, and some annulated, azulenes are used as substrates to determine the scope and limitations of this method. The bromoazulenequinones can be used as synthons, from which various azulenequinones can be derived by nucleophilic displacement. In a hope to encourage other chemists to develop new azulenequinone chemistry, we herein describe the process of the discovery, starting from the original motivation. In addition, we touch on remarkable and mysterious products whose structures remain undetermined and our speculation concerning their reaction paths. Some physical and chemical pro...

The redox potentials of 5,5' -biguaiazulene-3,3' (5H,5'H)-dione (a dimer of the monomeric 3-guaiazulenone radical) and its four unique autoxidation products were determined by cyclic voltammetry for a comparative study. The electrochemical behavior of these compounds is discussed.

The oligoethylene glycol derivatives having tropolonoid moieties at both terminals were synthesized. The diethylene to pentaethylene glycol derivatives formed Zn complex in an intramolecular fashion, which extracted metal picrates from the aqueous solution. The larger cooperativity was observed in the extractions of alkaline earth metal ions as compared with those of alkaline metal ions.

Oxidation of dimethyl 2-hydroxy-6-isopropylazulene-1,3-dicarboxylate (1a) with lead dioxide in acetic acid gave a 1,1′-bi-[2(1H)azulenone] derivative in good yield. The similar reaction of 5-isopropyl isomer of 1a gave two 1,1′-bi-[2(1H)azulenone] and a novel diethenoazupyrene derivative, as the first example, through 1,6′-coupling reaction followed by intramolecular Diels-Alder type cyclization.

The reaction of 7-isopropyl-4-methyl-1-azulenemethanol (1) with ethanol in ether yielded readily the novel compound, 1-ethoxymethyl-7-isopropyl-4-methylazulene (2), at low temperature in an ice bath, catalyzed by 20 % H2SO4. The following by-products were also obtained : 1) ether compounds : 1-ethoxymethyl-7-isopropyl-3- (7-isopropyl-4-methyl-1-azulenylmethyl) -4-methylazulene (2 B1); 1-ethoxymethyl-7-isopropyl-3- [7-isopropyl-3- (7-isopropyl-4-methyl-1-azulenylmethyl) -4-methyl-1-azulenylmethyl] -4-methylazulene (2 B1); 2) hydrocarbons : bis (7-isopropyl-4-methyl-1-azulenyl) methane (1 A1); 7-isopropyl-1, 3-bis (7-isopropyl-4-methyl-1-azulenylmethyl) -4-methylazulene (1 A2); and guaiazulene tetramers (1 A3) (1 A31 and 1 A32). All these compounds were isolated and purified by silica-gel column chromatography and confirmed by their spectroscopic (UV-vis, IR, 1H-NMR and MS) data.

The reactions of benzo[b]cyclohept[e][1,4]oxazine (9) with a 1.2 equivalent of α,ω-alkanediamines (2, n = 4—12) in ethanol at 80 °C afforded tropocoronands (5, n,n′ = 4,4—12,12) in a one-pot procedure and in high yields, while the reaction of 9 with an excess of 2 mainly gave tropopodands 12 (n,n′ = 4,4—6,6). The reactions of 9 with short-chain diamines 2 (n = 2,3) yielded bicyclic pyrazino or diazepino compounds as the main products. The reaction of 9 with ω-amino alcohol afforded the corresponding dihydroxy podands 23. The predicted pathways of the reaction of 9 with 2 were experimentally confirmed.

The stability and resonance energy of heterocycle-annulated 1-azaazulenes such as cyclohepta[4,5]pyrrolo[1,2-a]imidazole (5a) and 12-methoxy-5H-cyclohepta[4,5]pyrrolo[2,3-b][1,5]benzodiazepine (7) were elucidated by means of Aihara’s TRE and Gimarc’s TCS rule. These compounds are predicted to be aromatic with positive resonance energies and in conformity with the TCS rule.

The fundamental skeleton of the tropones possessing a unique heptagonal structure is predicted to be aromatic with positive resonance energies and conforming to the topological charge stabilization rule (TCS rule). Similarly, naturally occurring tropolones also nicely fit the theory that conformity to the TCS rule gives a stable molecular system. Thus, many of the troponoids so far synthesized and those occurring in nature are energetically very stable molecules as well as being synthetically very accessible. The TCS rule applies very well to the formation mechanism of heterocycle-fused tropones. It is very likely that there are various reaction paths in nature which are compatible with the TCS rule for the formatin of tropylium compounds having annulated heterocycles.

Oxidation of 4,6,8-trimethylazulene (1) with hydrogen peroxide in pyridine at 25°C for 18 h gave 4,6,8-trimethyl-1,5- and -1,7-azulenequinones, their 2-(4,6,8-trimethyl-1-azulenyl) derivatives, and 2,3-dihydro-4,6- and -4,7-dimethyl-2-(4,6,8-trimethyl-1-azulenyl)-1H-inden-1-ones in much higher yields than those by autoxidation of 1 in DMF at 120°C. The same oxidation of guaiazulene afforded sixteen separable products, among which there were three new dimeric condensates.

Various 3,3′-methylenebis azulenes were prepared in high yields upon treatment of 1-substituted azulenes with a solution of 0.1–0.2 wt% paraformaldehyde in glacial acetic acid at 25°C for 1 h. Thus, 1-methyl-, 1-isopropyl-, 1,5-diisopropylazulene, guaiazulene, and methyl 2-hydroxy-1-azulenecarboxylate readily provided the corresponding 3,3′-methylenebisazulenes, respectively. Acetic acid which had been refluxed with 5 wt% KMnO4 for 2 h and then distilled according to a purification method was found to contain 0.1–0.2 wt% formaldehyde and exert the same 3,3′-methylenebisazulene formation. 3,3′-Dideuteriomethyl-enebis(guaiazulene) was obtained by employing the similar distillate from acetic acid-d4.

An examination was made of the stability and formation pathways of azulenequinones produced by oxygenation in terms of Aihara’s graph theory of aromaticity and Gimarc’s TCS rule. In view of the TCS rule, the oxygen molecule in autoxidation first attacks C-1 of the azulenes, followed by the another oxygen molecule attacking at position n in 1-carbonylated azulenes to give azulenequinones.

Treatment of benzo[b]cyclohepta[e][1,4]oxazine with 1.2 equiv. of α,ω-diaminoalkanes (n=4-12) in ethanol at 80°C gave tropocoronands (n=4-12) in one step in high yields, while the reaction of 5 with an excess of 2 afforded tropopodands (n=4-6). The reactions of 5 with 2 (n=2,3) yielded bicyclic pyrazino or diazepino compounds in high yields. Coronands [14 (instead of 4a) and 4b (n=3)] were, however, obtained by the reaction of 5 with N-acetyldiaminoalkanes. The reaction of 5 with α,ω-amino alcohol afforded the corresponding podands

The stability and resonance energy of heterocycle-annulated 1-azaazulenes such as cyclohepta[4,5]pyrrolo[1,2-a]imidazole (5a) and 12-methoxy-5H-cyclohepta[4,5]pyrrolo[2,3-b][1,5]benzodiazepine (7) were elucidated by means of Aihara’s TRE and Gimarc’s TCS rule. These compounds are predicted to be aromatic with positive resonance energies and in conformity with the TCS rule.

The reactions of benzo[b]cyclohept[e][1,4]oxazine (9) with a 1.2 equivalent of α,ω-alkanediamines (2, n = 4—12) in ethanol at 80 °C afforded tropocoronands (5, n,n′ = 4,4—12,12) in a one-pot procedure and in high yields, while the reaction of 9 with an excess of 2 mainly gave tropopodands 12 (n,n′ = 4,4—6,6). The reactions of 9 with short-chain diamines 2 (n = 2,3) yielded bicyclic pyrazino or diazepino compounds as the main products. The reaction of 9 with ω-amino alcohol afforded the corresponding dihydroxy podands 23. The predicted pathways of the reaction of 9 with 2 were experimentally confirmed.

Treatment of benzo[b]cyclohepta[e][1,4]oxazine (4) with 1.2 equiv. of dipropylenetriamine (5a) in ethanol at 80 °C gave 6,7,8,9,11,12,13,20,- 21,22,23,25,26,27-tetradecahydrodicyclohepta[b,m][1,4,8,12,15,19]hexa- azacyclodocosine (7a). Similar reactions of (4) with N,N-bis(3-amino- propyl)methylamine (5b), bis(3-aminopropyl) ether (5c), 1,2-bis(2-amino- ethoxy)ethane (6b), and cystamine (6c) afforded similar tropocoronands (7b, 7c, 8a, and 8b), respectively, while the reactions of (4) with an excess of these amines gave the corresponding tropopodands (11a, 11b, 11c, 12a, and 12b). The reaction of (4) with diethylenetriamine (6a) yielded tricyclic compound (10) via bicyclic pyrazino compound (9). A single-crystal X-ray diffraction analysis of the nickel(II)-complex (13) obtained from (7a) was made

3-Bromo derivatives of 1,5- and 1,7-azulenequinones easily react with various nucleophiles to give 3-methoxy, phenoxy, p-nitrophenoxy, butylthio, butylamino, p-tolylamino, dimethylamino, 2-hydroxye...

Azulenequinones have been attracting great interest in recent years. After a brief introduction concerning an earlier study of azulenequinones we review recently developed areas of azulenequinone chemistry, which became possible by the discovery of a facile one-pot synthesis of azulenequinones, or their bromo derivatives, by means of the bromine oxidation of various azulene derivatives in an aqueous solvent. Various functionalized, and some annulated, azulenes are used as substrates to determine the scope and limitations of this method. The bromoazulenequinones can be used as synthons, from which various azulenequinones can be derived by nucleophilic displacement. In a hope to encourage other chemists to develop new azulenequinone chemistry, we herein describe the process of the discovery, starting from the original motivation. In addition, we touch on remarkable and mysterious products whose structures remain undetermined and our speculation concerning their reaction paths. Some physical and chemical pro...

3-Bromo-1,5-azulenequinone and 3-bromo-1,7-azulenequinone reacted with diphenylketene to give the corresponding tetraphenylazulenequinodimethane, which has both diphenylfulvene and diphenylheptafulvene structures. The protonation occurred at the diphenylmethylene group on the seven-membered ring to form a cycloheptatrienylium ion.

A synthetic route was developed for preparation of 2-aminotropone oximes 10–14, a new class of compounds, from tropolone 2; 2-methoxytropone imines 7–9 and tropylium salts 17 were generated as the key intermediates.

Azulenequinones gave dimers when they were irradiated with a high-pressure mercury lamp. In polar solvents, head-to-head dimers were predominant, whereas head-to-tail dimers increased in less polar solvents. From 3-methoxy-1,5-azulenequinone, four products were obtained, while bromoazulenequinones and 1,5-azulenequinone gave a single dimer. The product distribution was dependent on the polarity of solvents, substituents, and concentrations.

π-Electronic structures of 5H,11H+-cyclohepta[b]quinoxalinium ions and their O- and S-analogues were elucidated by means of 1H and 13C NMR spectra, electronic spectra, and theoretical calculations. Consequently, it was shown that these compounds had very stable aromatic characters with positive resonance energies and that the 6π-tropylium-6π-benzonoid form plays an important role for the π-conjugation structure.

Five isomeric benzo[b]cyclohept[e][1,4]oxazin-6∼10-ones (hereafter refered to as benzoxazinotropones) and bromobenzoxazinotropones were prepared almost quantitatively by the hydrolysis of the corresponding mono-, di-, and tribromobenzo[b]cyclohept[e][1,4]oxazines with refluxing acetic acid. On the basis of spectral data and theoretical calculations, benzo[b]cyclohept[e][1,4]oxazin-6∼9(11H)-ones are believed to exist in the keto form. These compounds gave respective methoxy- and acetoxybenzo[b]cyclohept[e][1,4]oxazines when reacted with diazomethane and acetic anhydride. On the other hand, benzo[b]cyclohept[e][1,4]oxazin-10(11H)-one was found to exist in a stable, intermolecularly hydrogen-bonded form and did not form acetoxylated or methylated compounds. Possible reaction pathways for the formation of these products are discussed.

The structures of abnormal reaction products (1:1 and 1:2) between 5-nitrosotropolone and arylamine are elucidated. The reaction of 5-nitrosotropolone with arylamine (e.g., aniline and p-toluidine) affords initially a bicyclic addition product, having 8-azabicyclo[3.2.1]octane system which could be formed by the attack of the amine on 4- and 1-positions of the tropolone ring. The adduct contains two isomers having syn and anti configuration with respect to the hydroxyimino group. These adducts easily isomerized under alkaline conditions to form lactams having the 6-azabicyclo[3.2.1]octane system, which may have been resulted from skeletal rearrangement of a seven-membered ring to a six-membered one. The former adducts, the 8-azabicyclo[3.2.1]octane system, further react with another mole of arylamine to give 1:2 products containing a lactam moiety via similar skeletal rearrangement.

The fundamental skeleton of the tropones possessing a unique heptagonal structure is predicted to be aromatic with positive resonance energies and conforming to the topological charge stabilization rule (TCS rule). Similarly, naturally occurring tropolones also nicely fit the theory that conformity to the TCS rule gives a stable molecular system. Thus, many of the troponoids so far synthesized and those occurring in nature are energetically very stable molecules as well as being synthetically very accessible. The TCS rule applies very well to the formation mechanism of heterocycle-fused tropones. It is very likely that there are various reaction paths in nature which are compatible with the TCS rule for the formatin of tropylium compounds having annulated heterocycles.

The steric compression-assisted proton dissociation in 3,7-disubstituted tropolones generates a new resonance hybrid of the tropolone, which contains the tropylium ion moiety and proton. This resonance hybrid model explains the observed unusual chemical properties of 3,7-disubstituted tropolones.

The lead(IV) oxide oxidation of various azulen-2-ol derivatives in acetic acid generates azulenoxy radicals via one-electron oxidation. The intermediates end up yielding recombined dimers, [1,1′-biazulene]-2,2′(1H,1′H)-dimers, as common type of products. In addition to these, hexacyclic cage dimers were obtained from 5-substituted azulen-2-ol derivatives. From dimethyl 2-hydroxyazulene-1,3-dicarboxylate, a hydroxyazulene having no substituent on the seven-membered ring was isolated a pair of dimethyl 2-hydroxy-4-[1,3-di(methoxycarbonyl)-2-oxo-1,2-dihydroazulenyl]azulene-1,3-dicarboxylate, but neither a cage dimer nor a 1,6-coupled dimer. The full structures of the dimers have been firmly established by an extensive X-ray crystallographic analysis and 13C NMR spectral comparisons of the key derivatives. Concerning the mechanism of the formation of the cage dimers, a [5+5] π cycloaddition followed by recombination of the resultant biallyl system is suggested.

An examination was made of the stability and formation pathways of azulenequinones produced by oxygenation in terms of Aihara’s graph theory of aromaticity and Gimarc’s TCS rule. In view of the TCS rule, the oxygen molecule in autoxidation first attacks C-1 of the azulenes, followed by the another oxygen molecule attacking at position n in 1-carbonylated azulenes to give azulenequinones.

Oxidation of 4,6,8-trimethylazulene (1) with hydrogen peroxide in pyridine at 25°C for 18 h gave 4,6,8-trimethyl-1,5- and -1,7-azulenequinones, their 2-(4,6,8-trimethyl-1-azulenyl) derivatives, and 2,3-dihydro-4,6- and -4,7-dimethyl-2-(4,6,8-trimethyl-1-azulenyl)-1H-inden-1-ones in much higher yields than those by autoxidation of 1 in DMF at 120°C. The same oxidation of guaiazulene afforded sixteen separable products, among which there were three new dimeric condensates.