Tropolones, hydrogenation

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]. 

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... 

Mo, O., Yafiez, M., 1998, Density Functional Theory Calculations on Hydrogen-Bonded Tropolone-(H20)2 Clusters , J. Phys. Chem. A, 102, 8174. 

The timescale of a microwave observation is ca 10 12s so that an average of the properties of the species in equilibrium (35) is obtained if the equilibrium occurs in a time shorter than this. The X-ray photoelectron spectra of intramolecularly hydrogen-bonded species in the gas phase have been studied in an attempt to obtain an instantaneous picture of the structure of these molecules. In this technique the ionisation of core electrons which occurs within 10 16s is observed. For malondialdehyde, 6-hydroxy-2-formyl-fulvene, 2-hydroxy-1,1,1,5,5,5-hexafluoropent-2-ene-4-one, 9-hydroxyphen-alenone [19], and tropolone [20], two peaks are observed in the Ou region of the photoelectron spectrum (Brown et al., 1979). If these molecules existed in the C2v form with a symmetrical hydrogen bond and equivalent oxygen... 

Reaction of tropolone with p-benzoquinone and spontaneous dehydrogenation yield 3-(p-benzoquinonyl)tropolone (106), which is hydrogenated and cyclized to give benzofurotropone 107 (62BCJ349, 62MI1). 

The bicyclic ketone (44), obtained from the Fe2(CO)9-promoted [3 + 4] cycloaddition reaction of a,a,a, a -tetrabromoacetone and 2-isopropylfuran followed by Zn-Cu couple reduction, has been converted to the naturally occurring troponoid, /3-thujaplicin (46) (75JOC806). Hydrogenation of (44), ether cleavage, bromination and dehydrobromination gave the tropone (45), an intermediate easily converted into the tropolone (46) by a standard procedure (Scheme 10). A related [3 + 4] cycloaddition reaction of oxyallyl metallic with furan has been used to assemble the antibiotic C-nucleosides (78JA2561). 

For an intramolecular OH O fragment, a strong hydrogen bond corresponds to R < 2.55 A and V < 8 kcal/mol. In this case, C and ft are close to unity and this corresponds to an intermediate case between the sudden and adiabatic regimes. Examples of such systems are malon-aldehyde, tropolon and its derivatives, and the hydrogenoxalate anion. 

Figure 6.5. Fluorescence excitation spectrum of jet-cooled tropolone. The broken lines indicate transitions for the high-wave-numbered tunneling doublet components. The bands due to the hydrogen-bonded complex between tropolone and water are indicated by the asterisks. (From Sekiya et al. [1990b].)...

The analysis of the IR spectrum of tropolone in a neon matrix [Redington, 1990], shown in Figure 6.7, is based on crystallographic data by Shimanouchi and Sasada [1973], This analysis reveals that the displacements of the nontunneling heavy atoms (by 0.07 A) are comparable to or even greater than the amplitudes of zero-point vibrations. The hydrogen transfer is coupled strongly with in-plane OO/C-O and C-OC/OC-C vibrations (qt and q2 coordinates, respectively). The... 

Because of intramolecular hydrogen bonding, the OH stretching frequencies of fused tropolones are distinctly lowered (as in tropolene itself) and lie at wave numbers between about 3350 and 3150 cm 1 [63BCJ173 65BCJ362 71CR(273)160 75MI1], The C=0 frequencies are lowered as well. 

Figure 1 An adsorption (top)-desorption (bottom) model for chiral induction on a zeolite surface, incorporating a reactant (tropolone alkyl ether, shown at the left), a chiral inductor (with four different substituents, at the right), and a cation (small ball on the surface). Tropolone s carbonyl and ether oxygens hydrogen-bond to chiral inductor, while its tt system interacts with zeolite s cation ion. ...

Figure 14 A cartoon representation of tropolone methyl ether and norephedrine included within a supercage under wet and dry conditions. The model helps to rationalize the difference in ee obtained under the two conditions. Dark circles represent the cations. Hydrogen bonding between the chiral inductor and interaction between the cation and TME are disturbed by water molecules.

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. 

In non-HBD solvents such as n-heptane, tetrachloromethane, diethyl ether, deuterio-tri-chloromethane, and dimethyl sulfoxide, tropolone transfers its proton to triethylamine to give an ion pair, which is in equilibrium with the non-associated reactants. There is no formation of a hydrogen-bonded complex between tropolone and triethylamine because of the fact that tropolone itself is intramolecularly hydrogen-bonded. The extent of the ion pair formation increases with solvent polarity. In polar HBD solvents such as ethanol, methanol, and water, this proton-transfer equilibrium is shifted completely towards the formation of triethylammonium tropolonate [171]. 

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