Site-Selective N-1 and C-3 Heteroarylation of Indole with Heteroarylnitriles by Organocatalysis under Visible Light

Accelerated photochemical reactions at oil-water interface exploiting melting point depression

Water can accelerate a variety of organic reactions far beyond the rates observed in classical organic solvents. However, using pure water as a solvent introduces solubility constraints that have limited the applicability of efficient photochemistry in particular. We report here the formation of aggregates between pairs of arenes, heteroarenes, enamines, or esters with different electron affinities in an aqueous medium, leading to an oil-water phase boundary through substrate melting point depression. The active hydrogen atoms in the reactants engage in hydrogen bonds with water, thereby accelerating photochemical reactions. This methodology realizes appealingly simple conditions for aqueous coupling reactions of complex solid molecules, including complex drug molecules that are poorly soluble in water.

Aqueous Flavin Photoredox Catalysis Drives Exclusive C3-Alkylation of Indolyl Radical Cations in Route to Unnatural Tryptophan Mimetics

One way to build chemical diversity into indoles is to oxidize them to indolyl radical cations (Ind•+). These intermediates can accept new functional groups across C2-C3 bonds or independently at C2. Less encountered is selective diversification at C3, a position plagued by competing dearomative side reactions. We disclose an aqueous photoredox-catalyzed method for transforming Ind•+ into C3-substituted tryptophan mimetics that uses water as a transient protecting group to guide site-selective C3 alkylation.

A Photosensitizer for N-O Bond Activation: 2,7-Br-4CzIPN-Catalyzed Difunctionalization of Alkenes with Oxime Esters

We developed 2,4,5,6-tetrakis(2,7-dibromo-9H-carbazol-9-yl)isophthalonitrile (2,7-Br-4CzIPN) as a new photosensitizer for the energy-transfer-driven N-O bond dissociation of oxime esters. In the presence of 2,7-Br-4CzIPN, difunctionalization of alkenes with oxime esters, including oxyimination, aminocarboxylation, and amidylimination, could afford a variety of versatile molecules in good yields with excellent regioselectivity, which widely occur in natural products and drugs. Our theoretical investigations and experiments have demonstrated that 2,7-Br-4CzIPN has unique photophysical properties, favorable triplet energy, and excellent photocatalytic activity.

Photochemistry Journey to Multielectron and Multiproton Chemical Transformation

The odyssey of photochemistry is accompanied by the journey to manipulate "electrons" and "protons" in time, in space, and in energy. Over the past decades, single-electron (1e^-) photochemical transformations have brought marvelous achievements. However, as each photon absorption typically generates only one exciton pair, it is exponentially challenging to accomplish multielectron and proton photochemical transformations. The multistep differences in thermodynamics and kinetics urgently require us to optimize light harvesting, expedite consecutive electron transfer, manipulate the interaction of catalysts with substrates, and coordinate proton transfer kinetics to furnish selective bond formations. Tandem catalysis enables orchestrating different photochemical events and catalytic transformations from subpicoseconds to seconds, which facilitates multielectron redox chemistries and brings consecutive, value-added reactivities. Joint efforts in molecular and material design, mechanistic understanding, and theoretical modeling will bring multielectron and proton synthetic opportunities for fuels, fertilizers, and chemicals with enhanced versatility, efficiency, selectivity, and scalability, thus taking better advantage of photons (i.e., sunlight) for our sustainable society.