Furanoheliangolides

In 1989 McDougal and co-workers presented an access to some racemic models of the 1 l-oxabicyclo-[6.2.1]undecane framework found in furanoheliangolides (the C/D ring system) [30]. The key reaction of their approach involved the ozonolysis of a functionalized oxa-bridged octalin 27, which provided the desired 1 l-oxabicyclo[6.2.1]undecane framework 28 (Scheme 3). Their synthetic approach started from the Diels-Alder reaction of 2-methyl-3-phenylthiofuran 23 with maleic anhydride. Namely, siteselective a-lithiation of vinyl sulfide 22, prepared from the conjugate addition product of thiophenol and acrolein, then quenching the... 

R.M. KING, H. ROBINSON. 1982. Furanoheliangolides and other compounds from Celea hymenolepis. Phytochemistry 21 2045-2048. 

Bohlmann, F., R.K. Gupta, R.M. King, and H. Robinson Naturally Occurring Terpene Derivatives. Part 448. Two Furanoheliangolides from Calea angusta. Phytochemistry 21, 2117 (1982). 

Paquette s [27] synthetic studies on sesquiterpenes furanoheliangolides such as zexbrevin possessing in their framework a 6,9-epoxycyclodeca[b]furan involve as the key synthetic steps high-pressure-promoted Diels-Alder reaction of 4-methyl-2-[(phenylmethoxy)methyl] furan 58 with 1-cyanovinyl acetate (Scheme 14). To suppress side reactions, hydroquinone was added. Near-quantitative formation of single diastereomeric adduct 59 was achieved at 12 kbar. Its conversion to tricyclic core 61 of furanoheliangolides was achieved after elaboration of the 7-oxabicyclo[2.2.1] heptene moiety and final [3,3] sigmatropic rearrangement of 60. 

Gershenzon, J., and T.J. Mabry Furanoheliangolides from Helianthus schweinit-ziL Phytochem. 23, 2557 (1984). 

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