Hydroperoxide and endoperoxide lactones from photooxygenation of 3-alkylidenedihydrofuran-2,4-diones.

3-Alkylidenedihydrofuran-2,4-diones 1 can be photooxygenated with O(2)/TBHP to hydroperoxides 3 which slowly decompose to diols 5. Stable endoperoxides 4 are best prepared by photooxygenation of 1 with 2 equiv of O(2) in the presence of CuSO(4) and p-TosOH following a nonradical mechanism. They are rapidly reduced by anhydrous FeBr(2) to give butenolide 9 indicating a potential antimalarial activity.