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A new method was developed for the synthesis of functionalized β tropolones based on acid catalyzed condensation of 2 methylquinoline derivatives with 3,5 di(tert butyl) 1,2 ben zoquinone and 4,6 di(tert butyl) 3 nitro 1,2 benzoquinone (14). The mechanism of the mul tistep reaction giving rise to β tropolones and their tautomerism were studied by quantum chemical methods (DFT B3LYP/6 31G**). The reaction of 2 methylquinoline derivatives containing the tertiary amino group at position 4 with quinone 14 is accompanied by the formation of derivatives of a new heterocyclic system, viz., 4,6 dioxo 2 azabicyclo[3.3.0]octa 2,7 diene N oxide. The molecular and crystal structures of two 5,7 di(tert butyl) 3 hydroxy 2 (quinolin 2 yl)tropolones and two dioxoazabicyclooctadiene N oxides, as well as of the preparatively isolated intermediate of the first condensation step and of the by product of the reaction were established by X ray diffraction.Due to the unique structure and properties of the seven membered tropolone ring and a broad spec trum of biological activities, natural compounds of the tropolone series (colchicine, colchamine, α , β , and γ thujaplicins, etc.) and their synthetic analogs have at tracted considerable attention. 1 Most of the already known tropolones belong to α tropolones, i.e., 2 hydroxy tropone derivatives. β Tropolones (3 hydroxytropones) are much less studied, although they include biologically active compounds, such as stipitatic acid (1) and puberu lic acid (2).The latter fact is primarily because convenient proce dures for the synthesis of β tropolone derivatives are lack ing. Unsubstituted β tropolone isolated as picrate was pre pared for the first time in very low yield by decarboxyla tion of 3,5 dimethoxycyclohepta 1,3,5 trienecarboxylic acid followed by bromination of the resulting 3,5 di methoxycycloheptatriene giving rise to β methoxytropone and demethylation of the latter. 2 A more general approach to the synthesis of β tropolone derivatives is based on the multistep transformation of 3,4,5 trimethoxybenzoic acid involving its reduction to 3,5 dimethoxy 1,4 dihydro benzyl alcohol, the preparation of its tosyl derivative, and the formation of a mixture of 1,3 dimethoxycyclo heptatrienes (as a result of thermal expansion of the six membered ring) followed by their oxidation. 3 Unsub stituted β tropolone was also prepared by photooxy genation of cyclohepta 1,3,5 triene with singlet oxygen followed by methanolysis of the resulting isomeric en * Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday.

Tropolones are promising organic compounds that can have important biologic effects.

Derivatives of 2-(2-indolyl)-cyclopenta­[b]­pyrrole-3,4-diones and pyrindino­[1,2-a]­indoles were synthesized by a new reaction of contraction of the o-quinone ring, and their structures were investigated by X-ray crystallography and nuclear magnetic resonance spectroscopy. The mechanisms of the reactions were suggested based on density functional theory calculations of the critical parts of the potential energy surfaces.

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SummaryA series of derivatives of 2-hetaryl-1,3-tropolone (β-tropolone) was prepared by the acid-catalyzed reaction of 2-methylbenzoxazoles, 2-methylbenzothiazoles and 2,3,3-trimethylindoline with 3,4,5,6-tetrachloro-1,2-benzoquinone. The molecular structures of the three representative compounds were determined by X-ray crystallography. In crystal and (as shown by the DFT PBE0/6-311+G** calculations) in solution, 2-hetaryl-4,5,6,7-tetrachloro- and 2-hetaryl-5,6,7-trichloro-1,3-tropolones exist in the NH-tautomeric form with a strong resonance-assisted intramolecular N–H···O hydrogen bond. The mechanism of the formation of 1,3-tropolones in the reaction of methylene-active five-membered heterocycles with o-chloranil in acetic acid solution has been studied using density functional theory (DFT) methods. The reaction of 2-(2-benzoxa(thia)zolyl)-5,6,7-trichloro(4,5,6,7-tetrachloro)-1,3-tropolones with alcohols leads to the contraction of the seven-membered tropone ring with the formation of 2-(2-benzoxa(thia)zolyl)-6-alkoxycarbonylphenols. The molecular structure of 2-(2-ethoxycarbonyl-6-hydroxy-3,4,5-trichlorophenyl)benzoxazole has been determined by X-ray diffraction. 2-(2-Benzoxa(thia)zolyl)-6-alkoxycarbonylphenols display intense green fluorescence with anomalous Stokes shifts caused by the excited state intramolecular proton transfer (ESIPT) effects.

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