Tropolone methyl ether

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-... 

Upon exposure to UV light, a-tropolone methyl ether (142), included within chirally modified Y zeolite, has been found to undergo 4 7r-electron disrotatory electrocyclic ring closure to afford " the bicyclic photo-isomer (143). 

The photochemical reactions of three a/3-unsaturated cyclic ketones have been reported. In these cases, it appears that the reaction is that of the olefinic group although the wavelength of the incident radiation is at the ultraviolet absorption of the carbonyl group. Photolysis of 2-cyclo-pentenone (16), carvone (XXXV) (7,12) and y-tropolone methyl ether... 

Simple tropolones also photoisomerize. 7-Tropolone methyl ether (Formula 6) gives the bicyclic photoisomer (Formula 7) on irradiation in aqueous solution (11). In similar fashion the simple a-tropolone methyl... 

The photochemical transformations of simple tropolone methyl ethers can be more complex than simple valence tautomerization. Irradiation of a-tropolone or its methyl ether (Formulas 16a,b) in aqueous solution in quartz vessels gives 4-oxo-2-cyclopentenylacetic acid (Formula 17a) or the methyl ester (Formula 17b) (15,16). 

Irradiation of a-tropolone methyl ether (Formula 8a) first gives the valence tautomer 9a, then the rearranged bicyclic product 18a, and finally the ester 19a (12). The reactions occur in sequence, and each stage requires light (the final transformation of Formula 18 to Formula 19 can also be achieved by acid). The initial reaction has ample precedent (11). The final transformation simply involves addition of water to the enol ether followed by a reverse aldol reaction. 

In principle, a similar tautomerism is possible in fused tropolones. Thus, O-methylation can lead either to one tropolone methyl ether (62BCJ808) or to two isomers, as in the case of anhydrosepedonin derivatives 418b and c (Scheme 112 69MI3). The yield of isomer 418c is very low, as expected. 

Dauben, W.G., Koch, K., Smith, S.L., and Chapman, O.L. (1963) Photo-isomerizahons in the a-Tropolone Series The mechanistic path of the a-tropolone methyl ether to methyl 4-Oxo-2-cyclo-pentenylactetate conversion. Journal of the American Chemical Society, 85, 2616-2621. 

Tropolone ethers have served as useful probes of asymmetric induction using several different supramolecular approaches [49]. Solid-state photolysis of 1 1 host-guest complexes of tropolone methyl ether 25 with (R,R)-( — )-4 caused disrotatory [2 + 2] photocyclization to 26 followed by transformation to afford... 

Furthermore, tropolone methyl ether 25 included in NaY and RbY zeolites that had been modified with optically pure norephedrine smoothly underwent enantioselective [2 + 2] photocyclization to afford the primary photoproduct 26 in around 40% ee (Scheme 7) [53]. The best results obtained are up to 78% ee... 

The inclusion complex 26, shown in Scheme 11, has been used as a host by Toda and coworkers to carry out a number of enantioselective reactions [231]. For example, irradiation of a 1 1 host-guest assembly of a-tropolone methyl ether 27 and (S,S)-( — )-26, in the solid state gave (lS,5R)-( — )-28 of 100% ee. The authors state that the high stereoselectivity is a result of the steric hindrance to disrotatory ring closure from one direction due to the structure of the host. This leads to the formation of only one enantiomer of the product. More details on this topic are available in Chap. 13. 

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.

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 course of total syntheses of the antimitotic alkaloid ( + )-colchicine and its biologically active analog 12 the rearrangement of 9 and 11 to tropolone methyl ether 10 and 12, respectively, assisted by ten equivalents of l,8-diazabicyclo[5.4.0]undec-7-ene, was used as the key step. ... 

For a mechanistic interpretation of the photoinduced valence isomerization of tropolone methyl ethers, Mukai and Miyashi have assumed that two excited state species 112 and 114 need to be considered. If 772 is stabilized by substituents in the tropolone ring, cyclization will give the product 113, but if 114 is more stable, product 115 will be favored. In the... 

Tropolones form chelate complexes with many metals and similarly, colchiceine, but not colchicine, affords a crystalline copper salt (324a, 324b). Like tropolone methyl ether, which is more soluble in water than is tropolone, colchicine is more water-soluble than the free tropolone, colchiceine. 

Decarboalkoxylation (5, 323). Greene and Crabbe have reported a novel prostanoid synthesis that employs a-tropolone methyl ether (1) as starting material. Irradiation of (1) leads to the bicycloheptadienone (2),which is con-... 

Tropolone is reduced by lithium aluminium hydride to cyclo-heptane-l,2-dione [262]. Under the same conditions its methyl ether rearranges to give benzaldohyde [262] alkyl substituted tropolone methyl ethers rearrange similarly [206]. 

Tropolone methyl ethers form hydrates and are more soluble in water and have higher boiling points than the parent tropolones [247, 280]. 

The methoxy bicycloheptadienone (135) was obtained [142] by irradiation of a-tropolone methyl ether which, after hydrogenation of the conjugated double bond, underwent cleavage by ozonolysis of the enol ether double bond to give the dimethyl acetal (136). The latter was then alkylated with ethyl 7-... 

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