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Di‐ and Trifluorinated 2‐Azidobenzimidazole Derivatives: Synthesis, Photooxygenation, and 19 F NMR Prediction
Author(s) -
Kanitz Nils E.,
Fresia Marvin,
Jones Peter G.,
Lindel Thomas
Publication year - 2021
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.202100603
Subject(s) - chemistry , photooxygenation , regioselectivity , singlet oxygen , nitrene , singlet state , fluorine 19 nmr , nitrobenzene , photochemistry , ring (chemistry) , computational chemistry , stereochemistry , nuclear magnetic resonance spectroscopy , organic chemistry , oxygen , excited state , physics , nuclear physics , catalysis
The photoreactivity of a series of hitherto unknown, multiply fluorinated 2‐azidobenzimidazole derivatives was investigated. The synthesis of the starting material includes regioselective p ‐defluorination of nitrobenzene derivatives employing Ogoshi's conditions. If the 6‐position was unsubstituted, irradiation in the presence of N‐protected amino acids at 300 nm (Rayonet) led to the formation of arylesters by oxygenation of the 6‐position in good to excellent yields and perfect regioselectivity. We did not observe any displacement of fluoride. If the 6‐position itself was fluorinated, alternative positions of the benzene portion were attacked. Mechanistically, the reaction proceeds through ring opening of the singlet nitrene to the cyanodiimine or via the iminobenzimidazolium ion. The availability of a set of fluorinated photo‐adducts prompted the quantum chemical calculation of their 19 F NMR chemical shifts. Even with the most suitable method investigated (ωB97XD/TApr‐cc‐pVDZ), deviations of up to 5 ppm from the experimental values were observed, underlining the importance of experimental measurements.