Germacrone lactones

FIGURE 11.5 Terpenoids, (a) The basic five-carbon units isopentane and isoprene. (b) The monoterpenes borneol and a-pinene. (c) A monoterpene lactone, nepetalactone. (d) A sesquiterpene, germacrone. (e) A triterpene, papyriferic acid, from paper birch. 

A further examination of the essential oil of Asarum caulescens Maxim, has resulted in the isolation and identification of caulolactone A (338) and B (339). Interestingly both these compounds co-occur with germacrone 4,5-epoxide (337), and in fact treatment of this epoxide With anhydrous aluminium chloride gives both these lactones in 10% and 8% yields respectively. Mechanistically this has been rationalized in terms of two conformations of the epoxide as depicted in... 

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