4- tropolone

Tropolone is known to undergo a tautomeric hydrogen shift shown below. In solution state H and 13C NMR spectra, averaged signals due to interconversion between the two tautomeric forms are observed. 

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Carboxylic acids —CO2H All types 3000-2500 as in tropolones OH stretching a characteristic group of small... 

Cyclo ddltion. Ketenes are ideal components ia [2 + 2] cycloadditions for additions to the opposite sides of a TT-system as shown ia the cyclobutane product (2) ia Figure 1. Electron-rich double bonds react readily with ketenes, even at room temperature and without catalysts. In conjugated systems, ketenes add ia a [2 + 2] fashion. This is illustrated ia the reaction foUowiag, where the preferential orientation of L (large substituent) and S (small substituent) is seen (40). This reaction has been used ia the synthesis of tropolone [533-75-5]. 

Tunneling splittings of different vibrational levels in the exeited A Bj elee-tronie state of the tropolon moleeule... 

Fig. 35. Normal modes of tropolon moleeule partieipating in tunneling tautomerization. Symmetry of modes is given in braekets. For the off-plane vibrations vjj and the symmetry plane is shown. The equilibrium bond lengths are indieated in the leftmost diagram.

In this case the parameters C and Q are of order of unity, and therefore they correspond to the intermediate situation between the sudden and adiabatic tunneling regimes. Examples are mal-onaldehyde, tropolon and its derivatives, and the hydrogen-oxalate anion discussed above. For intermolecular transfer, corresponding to a weak hydrogen bond, the parameters C, Q and b are typically much smaller than unity, and the sudden approximation is valid. In particular, carbonic acids fulfill this condition, as was illustrated by Makri and Miller [1989]. 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with A -bromosuccinimide from cyolo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - ... 

The present procedure, based on the last method, is relatively simple and uses inexpensive starting materials. Step A exemplifies the 2 + 2 cycloaddition of dichloroketene to an olefin, " and the specific cycloadduct obtained has proved to be a useful intermediate in other syntheses. Step B has been the subject of several mechanistic studies, and its yield has been greatly improved by the isolation technique described above. This synthesis has also been extended to the preparation of various tropolone derivatives. " ... 

Structure of tropones, tropolones, and tropylium salts with fused heterocyclic rings 95AHC(64)81. 

Tlie synthesis concludes by the route pioneered by Eschenmoser. Itromination of 47 proceeds at the position a to the tropolone I ing to give 48. Displacement of halogen by ammonia followed by liase hydrolysis of the tropolone methyl ether gives trimethyl-lolchicinic acid. Acetylation of the amine followed by reesteri-... 

In contrast to the resistance of cycloheptatriene systems (e.g., tropolone) towards hydrogenation, 3-benzothiepin 3,3-dioxide is readily hydrogenated at atmospheric pressure in the presence of Raney nickel to give l,2,4,5-tetrahydro-3-benzothiepin 3,3-dioxide in 78% yield.82... 

X-ray analysis of 2-methoxy-4-hydroxy-5//-l-benzazepin-5-one (a benzazatropolone), prepared by methylation of the corresponding 4-hydroxy-l-benzazepin-2,5-dione with Meerwein s reagent, demonstrates the presence of a planar seven-membered ring but, in contrast to tropolone, little 71-electron delocalization.17 Likewise, ll//-dibenz[f>,e]azepin-ll-ones display no significant aromatic character.18 In contrast, 7-chloro-8//-thieno[3,2-c]azepin-8-one (12) has azepine ring hydrogen resonances at 8.7 and 9.02 ppm that indicate a substantial contribution from the polar zwitterionic mesomer 13.19... 

Early COMT inhibitors, like gallates, tropolone and U-0521 (3, 4 -dihydroxy-2-methyl-propiophenone) have IC50 and IQ values in the micromolar range or higher but may still be practical in vitro tools. However, owing to unfavourable pharmacokinetics and toxicity their clinical use is not possible [1]. 

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