Green‐light-driven synergistic photo/biocatalysis for diamines synthesis

Chiral 1,2-diamines are common structural motifs in natural products, bioactive molecules, pharmaceuticals, chiral ligands, auxiliaries, and organocatalysts. Given their vital importance, great progress has been made to synthesize enantioenriched chiral vicinal diamines. Among these, direct enantioselective hydroamination of enamines is an appealing approach beneficial from the abundance, low cost and structural diversity. However, only a few chemocatalytic amination of enamines have been reported using chiral copper complexes, or chiral phosphoric acids, via two-electron electrophilic pathways. Despite advantages of biocatalysis in terms of selectivity, evolvability, and sustainability, biocatalytic hydroamination of enamines remains unexplored.

To expand enzyme reactivity, photoenzymatic catalysis has emerged as a versatile playground for testing asymmetric biotransformtions over the last few years. Driven by photoinduced single-electron radical pathways, many natural enzymes are reshaped to catalyze new-to-nature enantioselective radical reactions. So far, C/N/S-centered radicals have been successfully tamed by enzymes. Regarding highly reactive nitrogen-centered radicals (NCRs), the Hyster group has reported an intramolecular asymmetric hydroamidation of hydroxamic esters (including four intermolecular examples), in which fluorinated benzoyl (OBzF₅) was used as the leaving group. At the same time, Zhao’s group reported an enantioselective intermolecular radical hydroamination of styrenes using carbamates as radical precursors. Shortly after that, Zhao and coworkers further expanded the NCRs precursors to more challenging O-benzoyl hydroxylamines. NCRs in these transformations are derived from blue-light-induced N-O bonds cleavage and finally lead to chiral monoamines bearing a β to N benzylic stereocenter.

Recently, a research team led by Dr. Xiaoqiang Huang from Nanjing University, China presented the development of a dual bio-/photo-catalytic system for achieving enantioselective hydroamination of enamides, which can give easy access to diverse enantioenriched vicinal diamines. The organic dye RhB facilitates the initiation of NCRs with green light, ensuring milder reaction conditions and improved selectivity. These reactions progress efficiently and exhibit excellent enantioselectivities (up to >99% enantiomeric excess). All transformations achieved high yields and enantioselectivities, irrespective of the electronic nature or function group pattern of the substituents on the radical precursors. Furthermore, 0.1 mmol-scale reactions also proceeded well without change in stereoselectivity. Mechanistic studies uncovered the synergistic effect of the enzyme and the externally added organophotoredox catalyst Rhodamine B (RhB). This work demonstrates the effectiveness of photobiocatalysis to generate and control high-energy radical intermediates, addressing a long-standing challenge in chemical synthesis. The results were published in Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(24)60168-3).

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 15.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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