Preparation of Antimalarial Endoperoxides by a Formal [2 + 2 + 2] Cycloaddition.

A formal [2 + 2 + 2] cycloaddition reaction between a 1,3-dione, an olefin, and molecular oxygen mediated by light is reported, which delivers endoperoxides in good yield through the formation of two C-O and one C-C bond in one step. The resulting 1,2-dioxanes are stable compounds and can be further derivatized at the hemiacetal position via alkylation or acetylation. All compounds have been evaluated against Plasmodium falciparum, and the best compound displayed an IC50-value of 180 nM. A potential mechanistic rationale for the formation of these compounds is presented.