Di‐ and Trifluorinated 2‐Azidobenzimidazole Derivatives: Synthesis, Photooxygenation, and ¹⁹F NMR Prediction

Abstract

The photoreactivity of a series of hitherto unknown, multiply fluorinated 2-azidobenzimidazole derivatives was investigated. The synthesis of the starting material includes regioselective pdefluorination 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 6position in good to excellent yields and perfect regioselectivity. We did not observe any displacement of fluoride. If the 6position 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.

Aza-BODIPY Route to Ageladine A

“…In light of our interest in the photofunctionalization of 2-azidoimidazole derivatives, we intended to synthesize ageladine A ( 1 ) via the hitherto unknown azido analog. We also addressed the problem of chemo- and regioselective bromination of the pyrrole ring by altering its electronic properties through the formation of unprecedented boron complexes sharing an aza-BODIPY moiety.…”