Tropolone compounds

The tropolone compound Mn(0,0)2, where (0,0) = (98), was prepared from the ligand and Mn(OAc)2 in aqueous methanol, and, after drying, was sublimed. Undoubtedly, it is polymeric, but the details are unknown. 

The solid-state behaviour of tropolones indicates that hydrogen-bridged dimeric units of tropolone compounds dominate the solid-state behaviour of these molecules. 

A secondary aspect of the solid-state interactions in tropolone compounds is the ability to form rr-stacking units. This effect is due largely to the delocalisation of the cycloheptatriene ring system over the total molecule. Typical tt-tt interactions in benzene molecules range from 3.5. 0 A (mean 3.81 A) and with a nearly parallel orientation of 0 ° (mean 0.67°) between individual benzene molecules. In tropolone compounds the interaction is of order 3.72(3) A with an inter-planar angle between tropolone molecules 0.7(8)°. We present in Table 15-3 a selection of tropolone compounds [in total 21 entries]. 

Table 15-3. Comparative 77-stacking data for selected tropolone compounds...

Among the tropolone compounds found in nature are four tropolone-carboxylic acids,obtained from mold cultures.Two ofthese,stipitatonicadd(CXIV,R = COOH) and stipitatic acid (CXIV, R = H) have been obtained from Penicillium stipitatum (Bentley and Thiessen, 1963). Puberulonic add (CXV, R = COOH) and puberulic acid (CXV, R = H) were obtained from P. aurantio-virens, P. puberulum and P.johan-nioli as well as from strains of the P. cyclopium-viridicatum series (sources quoted in this paper). The infrared spectrum of the sodium salt of the anhydride of stipitatonic... 

Inhibitors of COMT are frequently competitive substrates, such as pyrogallol. No potent irreversible inhibitors of the enzyme are available. Figure 8 shows some of the substances which are effective inhibitors in vitro. 8-hydroxyquinoline is slightly more potent than pyrogallol as an inhibitor, but other metal chelating substances, such as EDTA, are inactive. The tropolone compounds, 4-methyl-tropolone and 4-isopropyltropolone ( -thujaplicin) are isosteric with catechols and can probably form a complex with magnesium ions and the active centre of the enzyme. 3,4 Dihydroxy-a-methylpropiophenone (U-0521) has recently been found to be a powerful competitive inhibitor both in vitro and in vivo. 

Another seven-membered ring that shows some aromatic character is tropone (44). This molecule would have an aromatic sextet if the two C=0 electrons stayed away from the ring and resided near the electronegative oxygen atom. In fact, tropones are stable compounds, and tropolones (45) are found in nature. However, analyses of dipole moments, NMR spectra, and X-ray diffraction measurements show that tropones and tropolones display appreciable bond alternations. ... 

Kassell (Takahashi et al., 1993) has described the activity of a novel tropolone U88999E in a rabbit model of cerebral vasosjrasm. U88999E inhibits lipid peroxidation and acts as a calcium antagonist. Kassell showed that the compound relaxed preconstricted arterial rings in vitro (potency slightly less than flunarizine or dil-tiazem) and that it reduced vasospasm of basilar arteries after rabbit subarachnoid haemorrhage (Takahashi etal., 1993). 

On the other hand, the anodic oxidation of 1,3,5-cycloheptatrienes is one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 2H -cyclohcpta h furan-2-oncs and azulenes14. 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

An example of the use of this approach in the disrotatory photocyclization of tropolone alkyl ethers is shown in Scheme 2. Thus, irradiation of the 1 1 complex of a-tropolone alkyl ether 10a with host compound 8 in the solid state gave photoproducts 11a of 100% ee and 12a of 91% ee in 11 and 26% yields, respectively [17]. 

Similar irradiation of the 1 1 complex of tropolone ether 10b and host compound 8 led to photoproducts 11b (100% ee) and 12b (72% ee) in 12 and 14% yields, respectively. The authors interpreted these reactions as follows disrotatory electrocyclic closure of tropolone derivative 10 to afford photoproduct 11 in the inclusion crystals occurs in only one direction owing to the steric hindrance of host 8. This interpretation appeared to be reasonable based on an examination of the X-ray crystal structure study of the inclusion complex [18]. Formation of keto-ester 12 takes place by a more complex mechanism... 

Tropones, tropolones, and tropylium salts have been known since the early 1950s. Today, they are counted among the most important classes of nonbenzenoid aromatic compounds. 

Heterocyclic Fused Tropones and Tropolones from Carbonyl and Heterocyclic Dicarbonyl Compounds (Scheme 8)... 

The synthesis of tropones, tropolones, and tropylium salts with fused heterocyclic rings forms the first part of a projected two-chapter sequence by G. Fischer (Leipzig, Germany). It is planned that the structure, reactivity, and applications of these compounds will be discussed in a further contribution in a subsequent volume. 

General methods for the preparation of niobium(v) and tantalum(v) complexes have been discussed and better synthetic routes to some known compounds have been described. [Nb(bpha) Cl], [Ta(bpha) Cl], and [NbO(t)3] (where bpha and t are the anions of benzoylphenylhydroxylamine and tropolone, respectively) have been prepared for the first time. NbClj or TaClj in methanol react with Hbpha to form the [M(bpha)4Cl] complexes. An aqueous solution of niobiumfv) which contains tartaric acid to prevent condensation of the hydrolysed metal species affords [NbO(t)3] with tropolone." " ... 

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