Biomimetic rearrangements of humulene
No abstract, first paragraph of introduction: Simple terpenoids have been known for many centuries as plant constituents whose fragrance commended them to the early investigators. Within this group of naturally-occurring compounds the C15 sesquiterpenes were of particular interest, largely as a result of their relatively high abundance. In 1895, Chapman isolated a new sesquiterpene, humulene (1), from oil of hops and by the preparation of various derivatives distinguished this hydrocarbon, previously called α-caryophyllene, from caryophyllene. The carbon skeleton of this hydrocarbon was established but the placement of the three olefinic bonds proved difficult. The structure was deduced correctly by degradative experiments and the analysis of the nmr spectrum suggested that all the double bonds were endocyclic and had a trans configuration. The structure was confirmed beyond doubt by an X-ray study of the bis-silver nitrate adduct.