Site-Selective C-O Bond Editing of Unprotected Saccharides.

Glucose and its polyhydroxy saccharide analogs are complex molecules that serve as essential structural components in biomacromolecules, natural products, medicines, and agrochemicals. Within the expansive realm of saccharides, a significant area of research revolves around chemically transforming naturally abundant saccharide units to intricate or uncommon molecules such as oligosaccharides or rare sugars. However, partly due to the presence of multiple hydroxyl groups with similar reactivities and the structural complexities arising from stereochemistry, the transformation of unprotected sugars to the desired target molecules remains challenging. One such formidable challenge lies in the efficient and selective activation and modification of the C-O bonds in saccharides. In this study, we disclose a modular 2-fold "tagging-editing" strategy that allows for direct and selective editing of C-O bonds of saccharides, enabling rapid preparation of valuable molecules such as rare sugars and drug derivatives. The first step, referred to as "tagging", involves catalytic site-selective installation of a photoredox active carboxylic ester group to a specific hydroxyl unit of an unprotected sugar. The second step, namely, "editing", features a C-O bond cleavage to form a carbon radical intermediate that undergoes further transformations such as C-H and C-C bond formations. Our strategy constitutes the most effective and shortest route in direct transformation and modification of medicines and other molecules bearing unprotected sugars.

Site-selective aromatic C-H λ3-iodanation with a cyclic iodine(iii) electrophile in solution and solid phases.

An efficient and site-selective aromatic C-H λ3-iodanation reaction is achieved using benziodoxole triflate (BXT) as an electrophile under room temperature conditions. The reaction tolerates a variety of electron-rich arenes and heteroarenes to afford the corresponding arylbenziodoxoles in moderate to good yields. The reaction can also be performed mechanochemically by grinding a mixture of solid arenes and BXT under solvent-free conditions. The arylbenziodoxoles can be used for various C-C and C-heteroatom bond formations, and are also amenable to further modification by electrophilic halogenation. DFT calculations suggested that the present reaction proceeds via a concerted λ3-iodanation-deprotonation transition state, where the triflate anion acts as an internal base.

Photosensitized, Energy-Transfer-Mediated Cyclization of 2-(1-Arylvinyl)benzaldehydes to Anthracen-9-(10 H)-ones.

A visible-light-induced photocatalytic intramolecular cyclization of 2-(1-arylvinyl)benzaldehydes is reported. The reaction is promoted in the presence of an IrIII photocatalyst and an amine base at room temperature under the irradiation of blue LEDs, affording 10-methylanthracen-9(10 H)-one derivatives in moderate to good yields with tolerance to various functional groups. A series of mechanistic experiments suggest that the reaction proceeds via energy transfer from the excited IrIII photocatalyst to the substrate to generate a diradical, which then undergoes 1,5-hydrogen shift, 6π electrocyclization, and aromatization leading to the cyclic product.