Preparation of 9a-Fluorinated Sesquiterpenic Drimanes and Evaluation of Their Antifeedant Activities

19 pages, figures, and tables statistics.The preparation of 9α-fluoro analogues of both natural and unnatural drimane-type sesquiterpenes is described. Their synthesis began with the initial preparation of methyl 8-keto- 12-nordriman-11-oate from β-ionone and entailed the electrophilic fluorination of C-9 for the stereoselective introduction of the fluorine atom. The drimane skeleton was completed from the intermediate 9α-fluoro-8-keto-12-nordrimane system by means of different reactions at the C-8 ketone carbonyl group, essentially Wittig methylenation, cyanohydrin formation or palladium-catalysed carbonylation of the corresponding enol triflate. Further manipulation of the functionalization derived from these key reactions allowed the preparation, among others, of 9α-fluorodrimanes, which are structurally and functionally related to albicanic acid, drimenin and olepupuane. Also described are the reactivities of some of the fluorine-containing systems prepared and a comparative study of the antifeedant activities of a selection of 9α-fluorodrimanes and the corresponding hydrogen analogues against several insect species with different feeding ecologies (Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi), which revealed a significant increase in the antifeedant activities of some of the fluorinated drimane analoguesPeer reviewe