Transition Metal-Free Supramolecular Photoredox Catalysis in Water: A Phenoxazine Photocatalyst Encapsulated in V-Shaped Aromatic Amphiphiles

An organic reaction in water using visible light as the only energy source is one of the goals of modern synthetic organic chemistry, and the encapsulation of a photoredox catalyst by a water-soluble molecular capsule is a promising strategy for it. Herein, we report on a transition metal-free supramolecular catalyst composed of V-shaped aromatic amphiphiles and a phenoxazine photoredox catalyst. A nanosized molecular capsule can efficiently uptake an organic photoredox catalyst in water, and the supramolecular catalysis can be tuned by choice of the host-guest combination. This system allows for the effective reduction of organic molecules under visible light irradiation and generates various carbon-centered radicals, such as ketyl radicals, aryl radicals, and trifluoromethyl radicals, for organic reactions in water. In particular, the present supramolecular catalysis turns out to be effective for pinacol couplings compared to the photoredox catalysis in organic solvents, and furthermore, it enables recycling of the catalyst and substrate-selective reactions, which are difficult to be achieved by the conventional photoredox catalysis in organic solvents.