The preparation of ester heterocycles mostly uses heteroatoms as nucleophilic sites, which are achieved by intramolecular substitution or addition reactions. Compound: 5-Amino-2-fluoropyridine( cas:1827-27-6 ) is researched.Quality Control of 5-Amino-2-fluoropyridine.Panov, Maxim S.; Voskresenska, Valentyna D.; Ryazantsev, Mikhail N.; Tarnovsky, Alexander N.; Wilson, R. Marshall published the article 《5-Azido-2-aminopyridine, a New Nitrene/Nitrenium Ion Photoaffinity Labeling Agent That Exhibits Reversible Intersystem Crossing between Singlet and Triplet Nitrenes》 about this compound( cas:1827-27-6 ) in Journal of the American Chemical Society. Keywords: azidodiethylaminopyridine nitrene nitrenium ion photoaffinity labeling agent reversible intersystem. Let’s learn more about this compound (cas:1827-27-6).
The photochem. of a new photoaffinity labeling (PAL) agent, 5-azido-2-(N,N-diethylamino)-pyridine, was studied in aprotic and protic solvents using femtosecond-to-microsecond transient absorption and product anal., in conjunction with ab initio multiconfigurational and multireference quantum chem. calculations The excited singlet S1 state is spectroscopically dark, whereas photoexcitation to higher-lying singlet excited S2 and S3 states drives the photochem. reaction toward a barrierless ultrafast relaxation path via two conical intersections to S1, where N2 elimination leads to the formation of the closed-shell singlet nitrene. The singlet nitrene undergoes intersystem crossing (ISC) to the triplet nitrene in aprotic and protic solvents as well as protonation to form the nitrenium ion. The ISC rate constants in aprotic solvents increase with solvent polarity, displaying a “”direct”” gap effect, whereas an “”inverse”” gap effect is observed in protic solvents. Transient absorption actinometry experiments suggest that a solvent-dependent fraction from 20% to 50% of nitrenium ions is generated on a time scale of a few tens of picoseconds. The closed-shell singlet and triplet nitrene are separated by a small energy gap in protic solvents. As a result, the unreactive triplet state nitrene undergoes delayed, thermally activated reverse ISC to reform the reactive closed-shell singlet nitrene, which subsequently protonates, forming the remaining fraction of nitrenium ions. The product studies demonstrate that the resulting nitrenium ion stabilized by the electron-donating 4-amino group yields the final cross-linked product with high, almost quant. efficiency. The enhanced PAL function of this new azide with respect to the widely applied 4-amino-3-nitrophenyl azide is discussed.
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