LongLarf

N-Carboxyanhydrides 1 (NCAs) are activated α-amino acid derivatives that can be modified in a minimum-waste process to give a variety of products. Photochemical deracemization using chiral catalyst 2 for stereochemical editing of the α-stereogenic center provided access to intermediates (R)-1 that can be immediately subjected to further transformations.

Abstract

Readily accessible, racemic N-carboxyanhydrides (NCAs) of α-amino acids underwent a deracemization reaction upon irradiation at λ=366 nm in the presence of a chiral benzophenone catalyst. The enantioenriched NCAs (up to 98 % ee) serve as activated α-amino acid surrogates and, due to their instability, they were directly converted into consecutive products. N-Protected α-amino acid esters were obtained after reaction with MeOH and N-benzoylation (14 examples, 70 %-quant., 82–96 % ee). Other consecutive reactions included amide (ten examples, 65 %-quant., 90–98 % ee) and peptide (three examples, 75–89 %, d. r.=97/3 to 94/6) bond formation. Limitations of the method relate for some NCAs to issues with solubility, photooxidation, and high configurational lability.

We report a selective photooxidation of commodity and postconsumer polyolefins to produce materials with in-chain ketones without using catalysts or expensive oxidants. Under mild conditions, yields reached up to 1.23 mol % of in-chain ketones, improving adhesion compared to unfunctionalized plastics. These ketones enable reaction with diamines, forming dynamic covalent polyolefin networks, upcycling mixed plastic waste into reprocessable materials with enhanced properties.

Abstract

Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in-chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol % of in-chain ketones were achieved. Installation of in-chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions.

Nature Catalysis, Published online: 17 October 2024; doi:10.1038/s41929-024-01234-0

The replacement of palladium with other metal catalysts in C–C bond-forming reactions is attractive in terms of costs and sustainability. Now an iron-based catalyst is successfully employed in the Suzuki cross-coupling of aryl chlorides with aryl boronic esters activated with tert-butyl lithium.

Nature Catalysis, Published online: 23 October 2024; doi:10.1038/s41929-024-01235-z

Thiamine, a common enzymatic cofactor, catalyses the benzoin condensation. From 1943, a panoply of mechanistic proposals were invoked to explain the intriguing transformation until two seminal papers by Ronald Breslow about 15 years after the discovery of this reaction helped resolve the mechanistic conundrum and heralded the birth of NHC-organocatalysis.