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Upon heating acetic acid containg a trace amount of coned sulfuric acid at 120 °C under nitrogen, 2-bromo-7-(2-hydroxyanilino)tropone (1a) gave 6-bromocyclohepta[b][1,4]benzoxazine (2a) as the main product and cyclohepta[b][1,4]benzoxazine, its 6,8-dibromo derivative and trace amounts of other mono-, di-, and tribromo compounds. This reaction became much more complex in the presence of oxygen. A similar bromine transfer was observed for 2-bromo-7-(dimethylamino)-, 7-(2-hydroxy-5-methylanilino)-, and 7-(2-methoxyanilino)tropone although the cite of the intermolecular bromine transfer depended upon the structures of the substrates and the reaction conditions. In contrast, 2a and 2-amino-5-bromotropone derivatives were completely stable towards the strong acid. Possible reaction pathways for this bromine transfer reaction are discussed.

The conjugative interaction between the two terminal groups in title quinarenone 2 and its chloro- and methoxy-derivatives were evaluated, proving that the diatropicity of the seven-membered ring is a little larger in 2 than in tropone. Some of these quinarenones are also found to exist in equilibrium with their oligomers and show unexpectedly low barriers of rotation about the intercyclic bond.

2-Chlorotropone reacted with o-aminobenzenethiol to give 2-(o-aminophenylthio)tropone, which readily cyclized in dilute methanolic HCl to afford the title benzothiazine (9). Although 9 was stable under basic conditions, its N-methyl cation reversibly afforded the ring-opened 2-[o-(methylamino)phenylthio]tropone in alkali. Oxidation of 9 with hydrogen peroxide in methanol underwent a rearrangement reaction to afford (exclusively) phenothiazine and its 1-formyl derivative. A similar H2O2 oxidation of 10-methoxycyclohepta[b][1,4]benzothiazine gave mainly methyl phenothiazine-1-carboxylate and 3-formyl-1-methoxy phenothiazine. Further oxidation of these products with hydrogen peroxide yielded thier S-oxides and S,S-dioxides. The reactivities of these cycloheptabenzothiazines are discussed in connection with those of the O- and N-analogues.

The application of Fischer’s indole synthesis to cyclohexanone 2-troponylhydrazone gave 1,2,3,4-tetrahydroindolo[2,3-b]tropone (II), which was then dehydrogenated to indolo[2,3-b]tropone (III). 8-, 10-Isopropyl-, and 7-bromoindolo[2,3-b]tropone (XIIa–c) were also obtained by a similar method. The treatment of 2-troponylhydrazones of cycloheptanone and N-benzylpiperidone with dilute sulfuric acid or PPA gave 2,3-pentamethylenepyrrolo[2,3-b]tropone (XIII) and 2-benzyl-1,2,3,4-tetrahydrocyclohept[b]pyrido[3,4-d]pyrrol-6(5H)-one (XIV) respectively. The reaction of III with phosphoryl chloride or thionyl chloride yielded 8-chlorobenzo[b]-1-azaazulene (XV), which was subsequently converted into a hydrazino derivative (XVI). The oxidative decomposition of XVI with copper sulfate in acetic acid afforded benzo[b]-1-azaazulene (XVII).

The reaction of 3-phenylpyrrolo[2,3-b]tropone (7) with phosphoryl chloride gave 8-chloro-3-phenyl-1-azaazulene (5). When 5 and 7 were treated with N-chlorosuccinimide, 2,8-dichloro-3-phenyl-1-azaazulene (6) and 2-chloro-3-phenylpyrrolo[2,3-b]tropone (8) were obtained respectively. 6 was also obtained from 8 by treatment with phosphoryl chloride. The reactions of 5 and 6 with nucleophilic reagents gave the corresponding substituted products (14a–m and 15a–m). 8-Hydrazino-3-phenyl-1-azaazulene (14m) and 2-chloro-8-hydrazino-3-phenyl-1-azaazulene (10), which had been obtained by the reaction of 5 and 6 with hydrazine hydrate, were decomposed by treatment with copper(II) sulfate in acetic acid to give 3-phenyl-1 -azaazulene (2) and 2-chloro-3-phenyl-1-azaazulene (11) respectively.

Three isomeric benzo-1, 4-thiazinotropones were obtained. Benzo-1, 4-thiazino[3,2-b]tropones substituted with the chloro, the bromo, the nitro or the acetamido group at the seven-membered ring were synthesized by the reaction of di- or trihalotropolone, or 3-bromotropolones with the nitro or the acetamido group, with o-aminothiophenol. The bromination of benzo-1, 4-thiazino[3,2-b]tropone (I) and its 8-isopropyl derivative (II) afforded 7- and/or 9-substituted compounds. In the case of nitration, 5-oxide and 5-oxide of 7-nitro derivative were obtained. The reaction of I or II with thionyl chloride unexpectedly gave the 7, 9-dichloro derivative of I, or four kinds of chloro derivatives of II.

Extensively reviewed are recent contributions of Japanese chemists to the development of troponoid chemistry over the past five years. The contents are divided into three parts: (i) reactions of rnonocyclic troponoids and their benz-analogues (benzologues) towards electrophilic and nucleophilic reagents as well as photochemical and thermal reactions; (ii) syntheses and reactions of heptafulvenes, sesquifulvenes, sesquifulvalenes and azulenes in addition to syntheses of troponoids and azulenes fused with heteroaromatic ring systems; (iii) syntheses of tropone and its simple derivatives and naturally occurring tropolones and finally theoretical discussions concerning the physical properties of troponoids. It is shown that many troponoid compounds react as cyclic polyolefins but some can undergo reactions, clearly typical of aromatic compounds. It is also shown that there remain many interesting and important problems in this field that await further studies.

The general observation is made that on electron impact the molecular ions of tropone derivatives eliminate carbon monoxide as a neutral molecule and the resultant ions behave as benzene derivatives. Exceptions from this rule can be explained in terms of the presence of specific structural features.

The dipole moments of tropone, 2-phenyltropone, tropolone methyl ether and their derivatives were measured in benzene solution at 25°. The increase of moment of tropone over that of cycloheptanone was adequately explained by mesomeric effect and an additional effect due to the formation of cycloheptatriene ring. The latter effect was supported by the theoretical moment for heptafulvene. The moments of various derivatives were compared with the theoretical data. The agreement between them confirmed the correctness of the position of substituents in these compounds already determined or inferred from the standpoint of organic syntheses. The apparent moment of tropolone methyl ether hydrate indicates that in benzene the hydrate dissociates into three separate molecules.

The oxidation of benzo-1, 4-thiazino[3,2-b]tropone and its 8-isopropyl derivative with hydrogen peroxide afforded the corresponding 5-oxides or 5, 5-dioxides. The stability of these oxides to heating, acid and alkali was examined. The bromination or nitration of these oxides gave mainly 9-bromo or 9-nitro derivatives. 7- or 9-Aminobenzo-1, 4-thiazino[3,2-b]tropones were obtained by the reduction of the corresponding nitro compounds.

The reaction of 2-bromo-7-methoxytropone with o-aminophenol gave 2-bromo-7-(o-hydroxyanilino)tropone (9), besides small amounts of cyclohepta[b][1,4]benzoxazin-6(11H)-one (10) and 15H-[1,4]benzoxazino[3′,2′ : 3,4]cyclohepta[2,1-b][1,4]benzoxazine (11). The heating of 9 with a strong acid afforded 6-bromocyclohepta[b][1,4]benzoxazine (13) quantitatively. On the other hand, the heating of 13 with o-aminophenol in ethanol gave 10, while in acetic acid a mixture of 10 and 11 was obtained. The mechanism of the formation of these products is discussed.

First ionization potentials are obtained for the four substances: tropolone (a) 9.86, (b) 9.83; tropone (a) 9.68, (b) 9.69; 2-aminotropone (a) 9.43, (b) 9.50; cyclohexanone (a) 9.91, (b) 9.83 (units being eV.). Classification symbols, (a) and (b), denote that the measurement was made either by the method of critical slope or by the linear extrpolation method. These results are consistent with the conclusions from other physical data under certain conditions.

The reaction of 2-bromo-7-methoxytropone with o-aminophenol gave 2-bromo-7-(o-hydroxyanilino)tropone (9), besides small amounts of cyclohepta[b][1,4]benzoxazin-6(11H)-one (10) and 15H-[1,4]benzoxazino[3′,2′ : 3,4]cyclohepta[2,1-b][1,4]benzoxazine (11). The heating of 9 with a strong acid afforded 6-bromocyclohepta[b][1,4]benzoxazine (13) quantitatively. On the other hand, the heating of 13 with o-aminophenol in ethanol gave 10, while in acetic acid a mixture of 10 and 11 was obtained. The mechanism of the formation of these products is discussed.

The reaction of 3-phenylpyrrolo[2,3-b]tropone (7) with phosphoryl chloride gave 8-chloro-3-phenyl-1-azaazulene (5). When 5 and 7 were treated with N-chlorosuccinimide, 2,8-dichloro-3-phenyl-1-azaazulene (6) and 2-chloro-3-phenylpyrrolo[2,3-b]tropone (8) were obtained respectively. 6 was also obtained from 8 by treatment with phosphoryl chloride. The reactions of 5 and 6 with nucleophilic reagents gave the corresponding substituted products (14a–m and 15a–m). 8-Hydrazino-3-phenyl-1-azaazulene (14m) and 2-chloro-8-hydrazino-3-phenyl-1-azaazulene (10), which had been obtained by the reaction of 5 and 6 with hydrazine hydrate, were decomposed by treatment with copper(II) sulfate in acetic acid to give 3-phenyl-1 -azaazulene (2) and 2-chloro-3-phenyl-1-azaazulene (11) respectively.

Cyclohepta[b][1,4]benzoxazine and 2-(o-hydroxyanilino)tropone were obtained by the reactions of 2-chloro- and 2-methoxytropone with o-aminophenol. A similar reaction with o-methoxylaniline gave 2-(o-methoxyanilino) tropone and 1-(o-methoxyanilino)-7-(o-methoxyphenylimino)-1,3,5-cycloheptatriene. The chemical and physical properties of cyclohepta[b][1,4]benzoxazine were discussed.

The application of Fischer’s indole synthesis to cyclohexanone 2-troponylhydrazone gave 1,2,3,4-tetrahydroindolo[2,3-b]tropone (II), which was then dehydrogenated to indolo[2,3-b]tropone (III). 8-, 10-Isopropyl-, and 7-bromoindolo[2,3-b]tropone (XIIa–c) were also obtained by a similar method. The treatment of 2-troponylhydrazones of cycloheptanone and N-benzylpiperidone with dilute sulfuric acid or PPA gave 2,3-pentamethylenepyrrolo[2,3-b]tropone (XIII) and 2-benzyl-1,2,3,4-tetrahydrocyclohept[b]pyrido[3,4-d]pyrrol-6(5H)-one (XIV) respectively. The reaction of III with phosphoryl chloride or thionyl chloride yielded 8-chlorobenzo[b]-1-azaazulene (XV), which was subsequently converted into a hydrazino derivative (XVI). The oxidative decomposition of XVI with copper sulfate in acetic acid afforded benzo[b]-1-azaazulene (XVII).

The tosylate (1) of tropone oxime undergoes a novel ring-opening reaction under mild conditions with secondary amines, alkoxides, and Grignard reagents affording stereoselectively 6-substituted (1Z,3Z,5Z)-hexa-1,3,5-triene-carbonitriles (2a–h) as sole products in high yields; these are easily converted into Z,Z,E-isomers (3a–h) with acids and further into E,E,E-isomers (4a–h) as the final form by stronger acid or by passing the solution over a column of alumina.

Cyclohepta[b][1,4]benzoxazine and 2-(o-hydroxyanilino)tropone were obtained by the reactions of 2-chloro- and 2-methoxytropone with o-aminophenol. A similar reaction with o-methoxylaniline gave 2-(o-methoxyanilino) tropone and 1-(o-methoxyanilino)-7-(o-methoxyphenylimino)-1,3,5-cycloheptatriene. The chemical and physical properties of cyclohepta[b][1,4]benzoxazine were discussed.

The tosylate (1) of tropone oxime undergoes a novel ring-opening reaction under mild conditions with secondary amines, alkoxides, and Grignard reagents affording stereoselectively 6-substituted (1Z,3Z,5Z)-hexa-1,3,5-triene-carbonitriles (2a–h) as sole products in high yields; these are easily converted into Z,Z,E-isomers (3a–h) with acids and further into E,E,E-isomers (4a–h) as the final form by stronger acid or by passing the solution over a column of alumina.