Selective endoperoxide formation by heterogeneous TiO2 photocatalysis with dioxygen

We report the selective formation of endoperoxides by aerobic TiO 2 photocatalysis through the cyclic addition of dioxygen and a non-conjugated diene , the first heterogeneous catalytic system for endoperoxide synthesis. This green protocol does not require any additive and the photocatalyst is abundant and recyclable, providing a yield up to 64% and >20:1 diastereoselectivity . Mechanistic investigations were carried out by using product analysis, kinetic studies , O-18 labelling experiments, electron-spin resonance and a set of quenching experiments. Superoxide (but not singlet oxygen , triplet oxygen or peroxide) is directly involved in the reaction cascade to form the endoperoxide product. The new findings may be helpful for future for designing eco-friendly and energy sustainable strategies for selective oxygenation reactions using semiconductors, O 2 and sunlight.