Hibiscones

Disubstituted- and 2,3,4-trisubstituted-furans are provided by oxidation or oxidation/acid-induced cyclization of the corresponding 2-butene-l,4-diols. These methods have been successfully employed for the synthesis of hibiscone C <00SL363> and cristatic acid . 

Cyclobutenes have been applied as latent functionality of 1,4-dicarbonyl systems. Photolysis of (466) gave a 1.5 1 mixture (60%) of (467a) and (467b), which were cleaved by ozone and subsequent reduction of the ozonides yielded the epimeric (468). Cyclization and dehydration process converted (468) to the furan (469) 160). Furan (469) was converted to hibiscone C in a few steps, 60). 

Hibiscones and various reddish-brown hibiscoquinones from Hibiscus elatus (Malvaceae) represent furanoid derivatives of eadinane. 

Ferreira M A, King T J, Ali S, Thomson R H 1980 Naturally occurring quinones. Part 27. Ses-quiterpenoid quinones and related compounds from Hibiscus elatus crystal structure of hibiscone C (gmelofuran). J Chem Soc Perkin Trans I 249-256... 

Other sesquiterpenes whose synthesis are worthy of mention are hibiscone C (38) (also known as gmelofuran), which is found in the heartwood of Hibiscus elatuSy and herbertene (40), isolated from the liverwort Herberta adunca. The synthesis of hibiscone by Koft and Smith" can be commended for its novel use of intramolecular [2 4- 2] photocycloaddition of the acetylenic enone (36) to set up the intermediate (37), whereas Prater s synthesis of herbertene is interesting, to say the least, since it involves a one-step acid-catalysed rearrangement of the alcohol (39) ... 

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