4-Pyridylnitrene and 2-pyrazinylcarbene

Abstract

SummaryBoth flash vacuum thermolysis (FVT) and matrix photolysis generate 2-diazomethylpyrazine (22) from 1,2,3-triazolo[1,5-a]pyrazine (24). FVT of 4-azidopyridine (18) as well as of 24 or 2-(5-tetrazolyl)pyrazine (23) affords the products expected from the nitrene, i.e., 4,4’-azopyridine and 2- and 3-cyanopyrroles. Matrix photolyses of both 18 and 24 result in ring expansion of 4-pyridylnitrene/2-pyrazinylcarbene to 1,5-diazacyclohepta-1,2,4,6-tetraene (20). Further photolysis causes ring opening to the ketenimine 27.

Spectroscopic Characterization of Nicotinoyl and Isonicotinoyl Nitrenes and the Photointerconversion of 4-Pyridylnitrene with Diazacycloheptatetraene

“…Given the calculated vertical transition at 543 nm ( f = 0.0002) for the expected nitrene 8 (Table S4 in the Supporting Information), the matrix was further irradiated with green light (532 nm). The corresponding IR difference spectrum (Figure B) demonstrates the sole depletion of the IR bands for nitrene 8 and the formation of ring-opening product N -(isocyano-vinyl)­ketenimine ( 13 ) indicated by the appearance of the IR band for the characteristic ketenimine moiety (NCC) at 2028.3 cm –1 , and it is also close to previously reported broad absorption in the range of 2028–2060 cm –1 in an Ar matrix . Consistent with the experimentally observed result in the photolysis of 4-azidopyrine, a full set of IR bands at 1869.2, 1545.4, 1335.2, 1274.8, 1216.2, 1109.5, 1021.5, 893.8, 828.9, 797.9, 711.5, and 659.4 cm –1 for diazacycloheptatetraene ( 9 ) was also observed.…”

“…In contrast to the full spectroscopy characterization of tetrafluoro- and tetrachloro-4-pyridylnitrenes formed in the photolysis of the corresponding azides in low-temperature matrices with UV, EPR, and IR spectroscopies, the parent 4-pyridylnitrene ( 8 ) was only detected by EPR spectroscopy, whereas the corresponding IR spectroscopy showed that the photolysis of 4-pyridyl azide mainly led to ring expansion to diazacycloheptatetraene ( 9 ). − In order to identify the nitrene intermediate 8 in our experiments, the decomposition of 4-pyridyl isocyanate ( 7 ), generated through flash vacuum pyrolysis of a mixture of 5 in N 2 (ca. 1:1000), was subjected to prolonged 193 nm laser irradiation, and the IR difference spectrum showing the decomposition of 7 is depicted in Figure .…”

Chemical Activation in Azide and Nitrene Chemistry: Methyl Azide, Phenyl Azide, Naphthyl Azides, Pyridyl Azides, Benzotriazoles, and Triazolopyridines

“…Here, the 3-isomer is expected to be the first-formed, but CA of ,68 kcal mol À1 ensures that a mixture is obtained. [65] The concerted mechanism for ring contraction (Fig. 5) is analogous to that proposed for phenylnitrene above, and the calculated amount of CA is also very similar (compare Figs.…”

Light-activated chemical probing of nucleobase solvent accessibility inside cells

“…Other dominant peaks in the spectrum were matched with the known products and intermediates of the Curtius rearrangement. Masses in negative control are matched to the azo products due to different reaction pathways from nitrene 30 . In addition, a peak with same retention time was detected in both samples of incubation of guanosine with NAz in the presence and absence of UV.…”