Total Synthesis of (-)-Penifulvin A, an Insecticide with a Dioxafenestrane Skeleton

Gaich, Tanja; Mulzer, Johann.   

Journal of the American Chemical Society  (2009),  131(2),  452-453.

Herein we report the first total synthesis of Penifulvin A, a sesquiterpenoid with a novel dioxa-fenestrane structure. Penifulvin A is a potent insecticide against the fall armyworm Spodoptera frugiperda which causes enormous damage in the US by consuming foliage of a variety of field crops. A five-step racemic and an eight-step enantioselective route to the natural product and the determination of its absolute configuration are described. The key step involves a meta-photocycloaddition, giving rapid access to the carbon skeleton of penifulvin A in a stereoselective fashion. Finally an oxidation cascade leads to the natural product. The synthetic route is free from protecting groups, scalable, and flexible so that a variety of analogues, among them penifulvins B−E, should be available for performing SAR tests in the insecticidal role.