Sesquiterpene quinones synthesis

Finally, Thiele acetoxylation of quinones, by treatment with acetic anhydride and sulfuric acid, is another excellent method of introducing functionality at an alkene carbon atom, for further synthetic elaboration (equation 50)196. This reaction was recently used as a key synthetic step in the total synthesis of metachromin-A, a useful sesquiterpene quinone moiety197. 

Schroder, J., Magg, C., and Seifert, K. (2000) Total synthesis of the marine sesquiterpene hydroquinones zonarol and isozonarol and the sesquiterpene quinones zonarone and isozonarone. Tetrahedron Lett., 41, 5469-5473. 

Almeida, W.P. and Correia, C.R.D. (1994) A total synthesis of the sesquiterpene quinone metachromin-A. Tetrahedron Lett., 35, 1367-1370. 

Laube, T., Bernet, A., Dahse, H.-M., Jacobsen, I.D., and Seifert, K. (2009) Synthesis and pharmacological activities of some sesquiterpene quinones and hydroquinones. Bioorg. Med. Chem., 17, 1422-1427. 

Addition of p-quinone ketals to olefins. The ketal 1 reacts with 1,2-dimethyl-cyclopentene in the presence of stannic chloride to afford, after reduction with sodium borohydride, 2 and its diastereomer 3. The major alcohol (2) was used by Biichi and Chu in a total synthesis of the sesquiterpene gymnomitrol (4). Several other syntheses of this substance have recently been reported. ... 

In 2012, Fukuyama s group reported a novel synthesis route to the spiro-p-lactonic sesquiterpene (-)-anisatin, and they also relied on the construction of a bicyclo[2.2.2]octane system via a DIB-mediated methoxylative phenol dearomatization followed by an intramolecular Diels-Alder reaction [127]. The homochiral phenolic dihydrobenzofuran propargyl ether 231 thus afforded, via the ort/io-quinone monoketal 232 and treatment of its intramolecular [4+2] epimeric cycloadducts with camphorsulfonic acid in MeOH, the bicyclo[2.2.2] octanedienone 234 as a single diastereomer (Fig. 56). Further transformation of 234 gave the vinyl 235, whose trisubstituted double btmd bridge was oxidatively cleaved by mild ozonolysis to furnish the ketoaldehyde 236, en route to (-)-anisatin [127]. 

See also Ling, X, Poupon, E., Rueden, E. J., and Theodorakis E. A., Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction, /. Am. Chem. Soc., 124, 2002. 

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