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Difluoromethylborates and muonium for the study of isonitrile insertion affording phenanthridines via imidoyl radicals

Konagaya, Kakeru, Huang, Yu-En, Iwami, Kazuki, Fujino, Tetsuya, Abe, Rikutaro, Parchment-Morrison, Reuben, Kojima, Kenji M., McKenzie, Iain and Ito, Shigekazu 2023. Difluoromethylborates and muonium for the study of isonitrile insertion affording phenanthridines via imidoyl radicals. Journal of organic chemistry 88 (13) , pp. 8042-8054. 10.1021/acs.joc.3c00056

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The 6-(difluoromethyl)phenanthridine unit is a highly attractive fluoroalkyl-substituted planar nitrogen heterocycle in pharmaceutical and agrochemical research. In this paper, we report that difluoromethylborates can be used as a source of difluoromethyl radicals for isonitrile insertion, leading to 6-(difluoromethyl)phenanthridines. Tuning the aryl substituents in the difluoromethylborates and oxidizing reagents enabled the synthesis of 6-(difluoromethyl)phenanthridines through the generation of difluoromethyl radical and spontaneous intramolecular cyclization of the CF2H-imidoyl radical intermediates. The presence of difluoromethyl radicals was experimentally confirmed, and the reaction mechanisms including imidoyl radical and prompt cyclization reactions could be supported theoretically. Furthermore, we obtained valuable information about the imidoyl radical intermediate by performing transverse-field muon spin rotation (TF-μSR) measurements of 2-isocyano-4′-methoxy-1,1′-biphenyl and using density functional theory (DFT) calculations to interpret the spectra. Muonium, a simple free radical, preferentially adds to the carbon atom of the isonitrile unit, yielding the corresponding imidoyl radical. The temperature dependence of the muon hyperfine coupling constant and the spin relaxation of the muoniated radical signal are compatible with the intramolecular cyclization of biaryl-substituted imidoyl radicals on the μs time scale.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: American Chemical Society
ISSN: 0022-3263
Date of First Compliant Deposit: 30 April 2024
Last Modified: 30 Apr 2024 09:50

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