3 years ago

Visible-Light-Mediated [4+2] Annulation of N-Cyclobutylanilines with Alkynes Catalyzed by Self-Doped Ti3+@TiO2

Visible-Light-Mediated [4+2] Annulation of N-Cyclobutylanilines with Alkynes Catalyzed by Self-Doped Ti3+@TiO2
Nan Zheng, Pingyun Feng, Chengyu Mao, Jiang Wang
We herein report a visible-light-mediated heterogeneous [4+2] annulation of N-cyclobutylanilines with alkynes catalyzed by self-doped Ti3+@TiO2. The self-doped Ti3+@TiO2 is stable under photooxidation conditions, easy to recycle, and can be used multiple times without appreciable loss of activity. Extensive mechanistic studies suggest that the annulation reaction is mediated by singlet oxygen, which is generated through the photosensitization of oxygen in the air by the self-doped Ti3+@TiO2. In contrast, the homogeneous variant catalyzed by a far more expensive iridium complex proceeds under an inert atmosphere, which indicates a different mechanism. The substrate scopes of the two processes are comparable. Doping is good: Self-doped Ti3+@TiO2 has been shown to be a visible-light-active and easily recyclable photocatalyst for [4+2] annulation of N-cyclobutylanilines with alkynes. Mechanistic studies reveal that upon visible light irradiation, self-doped Ti3+@TiO2 sensitizes oxygen in the air to singlet oxygen, which subsequently mediates the [4+2] annulation reaction.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701587

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