Tropolones hydrolysis

OH, SH, or tautomers, oxo, thioxo, respectively. b Tropone and acetyl carbonyl groups of 435,181, and 16 are likewise chlorinated. c Tropolone. Hydrolysis and decarboxylation. 

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. - ... 

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 addition to tropones, a few tropolones have been synthesized by reactions similar to those given in Scheme 2 and Table I. Hydroxyl substituents vicinal to carbonyl groups have been generated by hydrolysis of dibromo intermediates of type 5a (78BCJ3579) and by dehydrogenation of fused cyclohepten-3,4-diones [55LA(595)203] or their monoximes [70JPR(312)466] (by Pd-charcoal or spontaneously, respectively). 

MC15 when allowed to react with acidic aqueous solutions of tropolone (HT) gave the tetrakis(tropolonate) cations [MT4]+. Hydrolysis of the niobium derivative afforded [NbOT3], an oxygen-labeling experiment established that the oxo atom is abstracted from the displaced tropolone molecule. 

It is well known that colchicine exhibits U V maxima at 243 and 350 nm in CHC13 and ethanol. The latter is associated with the tropolonic moiety since it disappears on ring contraction to allocolchicine (12) which has a six-membered benzenoid ring C (25). TLC analysis of very small amounts of deacetylcolchicine and deacetylisocolchicine was made possible by making their DADF (dihydrofluorescein diacetate) derivatives (Fig. 7). Hydrolysis of the DADF derivatives with aqueous ammonia converted the... 

Eschenmoser s pyrone 38 on treatment with cyclopropenone ketal 39 in refluxing benzene afforded lactone 40 (73%). Lactone 40 on hydrolysis with acetic acid at 100°C afforded, after deprotection and decarboxylation, tropone 37 (70%). Introduction of the tropolonic hydroxyl group was achieved with hydrazine hydrate in ethanol, to give a mixture of deacetyl-colchiceinamides 41 (53%) and 42 (37%), followed by reaction with ethano-lic potassium hydroxide, which afforded tropolones 43 and 44, respectively. Tropolone 43 was converted to 44 which, therefore, became the major reaction product. Methylation of 44 gave a mixture of enol ether 18 and 45 which were separated by chromatography. 

The hydrolysis of the tropolone methyl ether 360 with concentrated HCl in boiling EtOH results in the hydroxyfluorenone 361 (equation 172) °. Thermal rearrangement with loss of sulfur dioxide occurs on heating the y-sultones 362 in dioxane, DMSO, dioxane-water or THE at 90 °C for 6-10 h to give 90% of the styrene derivatives 363 in a highly stereospecific manner (equation 173). ... 

In the ester series the acid-catalysed cyclisation of the alcohol (452, R=C00Me) gives a mixture of the By-unsaturated ester (455, R=C00Me) and its aB-unsaturated isomer, both of which give the same tropolone on oxidation and this yields (456) on hydrolysis and decarboxylation. 

This compound, m.p. 196-198°, was isolated from the corms of C. autumnale (294). No analytical data were presented, but a tropolone ring was indicated by a positive ferric chloride test after hydrolysis with dilute acid. 

Following a route previously developed for the synthesis of deacetamidocolchicine, (+)-colchicine has been synthesised from (136 R = R = OMe), which was hydrolysed by acid to (136 RR = 0) and this was cyclised by boron trifluoride etherate to the acid (137). Ring-expansion of the methyl ester of (137) with trifluoroacetic acid gave a mixture of (138) and the isomeric ag-unsaturated ester, both of which, on oxidation, gave the tropolone (139), hydrolysis and decarboxylation of which gave deacetairaido-isocolchicine. Hydrolysis of (139) and treatment with diphenyl-... 

Rearrangement to the proper orientation of the tropolone system was accomplished by reaction with p-toluenesulfonic acid in pyridine and then treatment with ammonia to form LXXIV, whose UV-spectrum was identical with that of colchicinamide. Hydrolysis converted LXXIV to desacetamidocolchiceine (LXII), identical with the authentic degradation product (mixed melting point and spectra). 

A related reaction type is the high pressure (6.2 kbar) Diels-Alder reaction of 2-pyrones with cyclopropenone ketals 16 to give isolable bicycloadducts 17, which then undergo cycloreversion, electrocyclic rearrangement, and ketal hydrolysis leading to tropones. Tropolones also have been formed in this way. This tropolone annulation chemistry was the partial subject of a review in 1990, and it was exploited in the syntheses of some naturally occurring tropoloisoquinolines 18-20. ... 

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