Naturally Occurring Spirocyclic Ketals from Lactones. 3

Article abstract of DOI:10.1021/jo00137a020

Our earlier methodology for the synthesis of 1,6-dioxaspiro<4.4>nonane and 1,6-dioxaspiro<4.5>decane derivatives has been applied to the synthesis of substances found in the mandibular gland secretions of Andrena bees.Use of optically active propylene oxide as a precursor gave 7-methyl-1,6-dioxaspiro<4.5>decane, reported from Andrena and Vespula species, in 80percent optical purity as shown by 13C NMR spectroscopy with a chiral shift reagent.Adaptations of the method allowed synthesis of a tetramethyl-1,6-dioxaspiro<4.4>nonene found in Japanese hop oil and of exogonic acid, a resin constituent of the Brazilian tree Ipomoae operculata (Martin).We have also simplified our synthesis of chalcogran, 2-ethyl-1,6-dioxaspiro<4.4>nonane, by using γ-caprolactone and the lithium reagent prepared from 3-bromo-1-propyl 1-ethoxyethyl ether.