Eudesmane terpenes

SCHEME 17.9. Asymmetric total synthesis of eudesmane terpenes (65-68). 

Scheme 38 Enamine-catalyzed Michael addition for the synthesis of the eudesmane terpene...

Chen K, Baran PS (2009) Total Synthesis of Eudesmane Terpenes by Site-Selective C-H Oxidations. Nature 459 824... 

Ghen K, Baran PS. Total synthesis of eudesmane terpenes by site-selective G H oxidations. Nature 2009 459 824— 828. 

The diastereosclectivity in this particular cyclization was exploited in a number of direct syntheses of terpenes from the eudesmane type (see Table 2). By this technique tricyclic compounds can be synthesized generating three new asymmetric centers55. 

Fig. 38 Examples of molecules prepared following new concepts in total synthesis (a) intricarene (220) generated by protective group-free synthesis and (b) late-stage site-selective C-H oxidations to generate eudesmane-type terpenes like 222 or (c) to prepare the hydroxylated artemisinin derivative 223...

More recently " the naturally occurring cyclopropenones 9 and 11 have been isolated from Telekia speciosa. The terpene derivative with the 7a-H, compound 9, is also found in Lychnophora passerina together with an isomer tentatively assigned as the Ip-H epimer 10 and not the eudesmane derivative 11 as initially thought. 

Of the rearranged eudesmanes, eremophilanes (216) are most prolific ( 150 derivatives). The subject was reviewed in 1977 (314). Two stereochemical classes, 239 and 240, have been recognized in principle, these are related to the eudesmane (222) and intermedeane types (225), respectively. The first member of this class to be characterized was eremophilone (241), which occurs in the wood oil of the Australian tree Eremophila mitchelli, along with other related compounds. This was the first terpene structure not consistent with the isoprene rule and Robinson (327) invoked a 1,2-methyl shift from a eudesmane precursor to rationalize this structure. (-)-Eremoligenol (242) is a component of roots of Ligularia fischeri, while isovalencenic acid (243) has been isolated from vetiver oil. (-h)-Nootkatone (244) was first isolated from the heartwood of Alaska-cedar... 

Eudesmanes and eudesmanolide derivatives 89-93 isolated from or chemically obtained from isolated terpenes from Sideritis sp. have been used for biotransformation by Curvularia lunata or Rhizopus nigricans. Beside (sometimes predominant) reduction reactions, hydroxylations occur in substantial yields at the methyl groups of the side chain in 89 [121] C-1, C-2, and C-4 of the A ring in 90 and 91 [122], and on various positions such as C-1, C-4, or C-8 in 92 [123] and 93 [124,125]. 

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