Tropolone methyl ether rearrangement

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]. 

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. 

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. ... 

Upon photolysis, tropolone alkyl ether 7 undergoes intramolecular 4n elect-rocyclization to afford chiral bicyclo[3.2.0]heptadienone 8, which rearranges to compound 9 upon prolonged irradiation (Scheme 6). The photocyclization of CD-complexed tropolone methyl ether 7a was hrst studied by Takeshita and coworkers [46]. They found that the formation of CD complex improves the yield of the optically active product 8a, but the ee value was not quantitatively determined. 

The transformation of 7,7-diMeO-CHT to a-, and y-tropolones is also achievable by using anodic oxidation in the key step (equation 18), namely the electrochemical oxidation of an isomeric mixture of diMeO-CHTs prepared by the thermal rearrangement of 7,7-diMeO-CHT yields a mixture of methyl ethers of ji- and y-tropolones. On the other hand, the thermal rearrangement of the ethylene acetal of tropone gives 3,4-dioxyethylene-CHT as a single product due to the difficulty of formation of other isomers, and it yields the ether of a-tropolone upon anodic oxidation. 

Cyclopropanation.1 The key step in a biomimctic synthesis of (i)-colchicine (4) is a regio- and stereoselective reaction of the tricyclic I, prepared in several steps from 5-bromo-2-methoxyphenol, with dimethylsulfoxonium methylide to give a single product (2) in 75% yield. When treated with trifluoroacclic acid at 25°, this product rearranges in 89% yield to the a-tropolone O-methyl ether 3. This product is converted into ( )-co chicine (4) in four known steps. 

Five-membered Rings. Irradiation of tropolone a-methyl ether (83) is known to give the rearrangement product (84) in high yield. This has been used as a starting material for the synthesis of 11-deoxyprostaglandin Ei (85) (Scheme 27). ... 

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