The redox-neutral addition of α-C–H bonds of acetonitrile and acetone to styrenes was enabled via the hydrogen-atom transfer from relatively acidic and water-miscible C(sp3)–H bonds to an aqueous hydroxyl radical...

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A metal-free, biomimetic catalytic protocol for the cyclization of N-(2-hydroxyethyl)­amides to the corresponding 2-oxazolines (4,5-dihydrooxazoles), promoted by the 1,3,5,2,4,6-triazatriphosphorine (TAP)-derived organocatalyst tris­(o-phenylenedioxy)­cyclotriphosphazene (TAP-1) has been developed. This approach requires less precatalyst compared to the reported relevant systems, with respect to the phosphorus atom (the maximum turnover number (TON) ∼ 30), and exhibits a broader substrate scope and higher functional-group tolerance, providing the functionalized 2-oxazolines with retention of the configuration at the C(4) stereogenic center of the 2-oxazolines. Widely accessible β-amino alcohols can be used in this approach, and the cyclization of N-(2-hydroxyethyl)­amides provides the desired 2-oxazolines in up to 99% yield. The mechanism of the reaction was studied by monitoring the reaction using spectral and analytical methods, whereby an 18 O-labeling experiment furnished valuable insights. The initial step involves a stoichiometric reaction between the substrate and TAP-1, which leads to the in situ generation of the catalyst, a catechol cyclic phosphate, as well as to a pyrocatechol phosphate and two possible active intermediates. The dehydrative cyclization was also successfully conducted on the gram scale.

Efficient N‐methylation is highly required for the synthesis of N‐methylated α‐amino acids and peptides, both of which are essential motifs in biochemical applications. Herein, we report a photocatalytic system using metal‐loaded titanium dioxide in methanol under near‐UV light irradiation for N‐methylation of α‐amino acid or its derivatives at ambient temperature without wasteful stoichiometric reagents. The present method enables the N‐methylation of twenty kinds of α‐amino acid motifs found in proteins in the human body, whether polar/non‐polar or acidic/basic functional groups are embedded in the substrates. Dipeptides also undergo the N‐methylation at the N‐terminal while the peptide bond and carboxylic acid remain intact. Most of the N‐methylated products can be isolated through simple filtration and concentration without tedious purification processes such as an aqueous workup and column chromatography.

Despite the continuing popularity of radical reactions in organic synthesis, much remains to be explored in this area. Herein, we describe how spatiotemporal control can be exerted over the formation and reactivity of divergent exchangeable formamide radicals using nickel complexes with a semiconductor material (TiO₂) under irradiation from near-UV–Vis light. Depending on the bipyridine ligand used and the quantity of the nickel complex that is hybridized on or nonhydridized over the TiO₂ surface, these radicals selectively undergo substitution reactions at the carbon center of carbon–bromine bonds that proceed via three different pathways. As the scalable production of formamides from CO₂ does not produce salt waste, these methods could add a new dimension to the search for carbon neutrality through the indirect incorporation of CO₂ into organic frameworks.