- Selective endoperoxide formation by heterogeneous TiO2 photocatalysis with dioxygen
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We report the selective formation of endoperoxides by aerobic TiO2 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, O2 and sunlight.
- Qiao, Xiaofeng,Biswas, Subharanjan,Wu, Wenli,Zhu, Feng,Tung, Chen-Ho,Wang, Yifeng
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- Endoperoxide synthesis by photocatalytic aerobic [2 + 2 + 2] cycloadditions
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Structurally novel endoperoxides can be sythesized by the photocatalytic cyclotrimerization of bis(styrene) substrates with molecular oxygen. The optimal catalyst for this process is Ru(bpz)32+, which is a markedly more efficient catalyst for these photooxygention reactions than conventional organic photosensitizers. The 1,2-dioxolane products are amenable to synthetic manipulation and can be easily processed to 1,4-diols and γ-hydroxyketones. An initial screen of the biological activity of these compounds reveals promising inhibition of cancer cell growth.
- Parrish, Jonathan D.,Ischay, Michael A.,Lu, Zhan,Guo, Song,Peters, Noel R.,Yoon, Tehshik P.
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supporting information; experimental part
p. 1640 - 1643
(2012/05/04)
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