Synthesis of Macrocyclic Terpenoid Hydrocarbons by Intramolecular Carbonyl Coupling: Bicyclogermacrene, Lepidozene, and Casbene

Article abstract of DOI:10.1021/jo00231a012

Total syntheses of two germacrane sesquiterpenes, bicyclogermacrene (1) and lepidozene (2), and of the cembrane sesquiterpene casbene (3) are discussed.Bicyclogermacrene and lepidozene were prepared in seven steps from geranylacetone by routes that involve titanium-induced cyclizations of cis- and trans-2,2-dimethyl-3-<3-methyl-7-oxo-3(E)-octenyl>cyclopropanecarbaldehyde, respectively. (+)-Casbene was prepared from (+)-2-carene and 6-methyl-5-hepten-2-one by a route whose key steps were the palladium-catalysed cross-coupling of vinylic iodide 31 with homoallylic organozinc reagent 32 and titanium-induced cyclization of cis-2,2-dimethyl-3-<3,7-dimethyl-11-oxo-3(E),7(E)-dodecadienyl>cyclopropanecarbaldehyde (16).