Boronic acids are a class of building blocks widely used in organic synthesis and are getting more important in medicinal chemistry as kinase inhibitors or boron-carried agents for boron neutron capture therapy (BNCT). The team led by Prof. Zhibo Liu at the Department of Applied Chemistry of the College of Chemistry and Molecular Engineering,Peking Universityhas reported an innovative direct decarboxylative borylation methodology of carboxylic acids catalyzed by visible light. The methodology adopts a mild and efficient condition conducted by iridium complex and cobalt complex as a dual-metal photocatalytic system. The reaction can be conducted efficiently in the air with broad functional group compatibility. A systematic mechanism study shows that the redox potential of carboxylic acid decreases through the hydrogen bond activation of carboxylic acid by tetramethylguanidine (TMG). This study is recently published in Nature Communications entitled "Photocatalytic Direct Borylation of Carboxylic Acids".
Fig. 1Photocatalytic direct borylation of carboxylic acids enabled by biomimetic activation.
It is attractive to prepare high value-added boronic acids from cheap and plentiful carboxylic acids. To date, the decarboxylative borylation of carboxylic acids is generally realized throughone extra step involving synthesized redox-active ester intermediate, or in-situ generated carboxylic acid covalent derivatives above 150°C reaction temperature.Due to the high redox potentialof carboxylic acids, a pre-activation process via corresponding carboxylic acid derivatives is needed for the decarboxylative borylation process according to previously reported work. For instance, Baran group and Aggarwal group (2017) have reported the decarboxylative borylation methodology through pre-preparation of corresponding NHPI eaters, while Szostak group (2018) have completed decarboxylative borylation via in-situ generation of corresponding anhydride intermediates at high temperature (Fig. 1a).
Inspired by the biomimetic approaches of enzymatic decarboxylation (Fig. 1b), Zhibo Liu grouphas reported a direct decarboxylative borylation method of carboxylic acids without any extra stoichiometric additives or synthesis steps. This operationally simple process produces CO2 andcan be accomplishedunder mild visible-light catalysis conditions, in terms of high step economy and good functional group compatibility(Fig. 1c). A conceptually different guanidine-basedbiomimetic active decarboxylative mechanismis proposed andthe mechanistic studies have also been conducted, which may extend to wider applications beyond borylation.
Dr. Qiang Wei from Liu Group is the first author, and Prof. Zhibo Liu is the corresponding author. This research was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology of the People's Republic of China, the Beijing Municipal Natural Science Foundation, the Peking-Tsinghua Center for Life Sciences and the Beijing National Laboratory for Molecular Sciences.
Original link for the paper: https://www.nature.com/articles/s41467-022-34833-1
