Non-famesyl Sesquiterpenoids

There are relatively few sesquiterpenoids which cannot be derived from a farnesyl precursor either directly or indirectly. Recent examples of this rare group are furoventalene (403), the keto-lactone (404), the phenol (405), and the revised structure of humbertiol (406). Proposed biogenetic schemes for these compounds involve the combination of a C o monoterpene unit (either acyclic or cyclic) with a C5 unit (e.g., dimethylallyl pyrophosphate). 

Weinheimer and P. H. Washecheck, Tetrahedron Letters, 1969, 3315. F. Bohlmann, C. Zdero, and M. Grenz, Tetrahedron Letters, 1969, 2417. F. Bohlmann and M. Grenz, Tetrahedron Letters, 1969, 1005. 

Finally, it has been reported that a sesquiterpene compound, bilobalid A, isolated from the leaves of the Ginkgo tree, appears to have structural similarities with the unusual diterpenoid ginkgolides, in which one of the y-lactone rings (ring f) has been removed. 

This chapter is subdivided into sections, each based on the major skeletal types of diterpenes. A widely circulated report on the Common and Systematic Nomenclature of Cyclic Diterpenes by J. W. Rowe, contains proposals made to I.U.P.A.C. for the naming and numbering of diterpenes. Although these proposals have not yet been officially accepted, they are applied in a number of publications and have been used in the present Report. 

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