Photochemical isomerization of 2H-imidazoleN-oxides

Synthesis of Three‐Membered and Four‐Membered Heterocycles with the Assistance of Photochemical Reactions

“…The oxaziridines obtained here were not likely to undergo reverse isomerization to the starting nitrones (Scheme ) .…”

“…The nature of solvent and conjugation influenced the stability of products obtained from isomerization of conjugated nitrones. The photolysis of 2H-imidazole-1,3dioxides in nonpolar solvents afforded isomerization products of one of the nitrone groups, which were successively isomerized to starting substrates [79]. Among more stable products of isomerization of both nitrone groups in products, the highly strained cis-isomer was isomerized to the starting dinitrone in acetic acid on continuous heating (Scheme 20) [78].…”

Revealing the Unexplored Mechanism of Photochemical Oxaziridine Conversion Process of 2H‐imidazole 1‐oxides

“…The well-known spin-trapping nitrones, 2,2,4-trimethyl-2Himidazole 1-oxide (TMIO) and 2,2-dimethyl-4-phenyl imidazole 1-oxide (DMPIO) belong to this category. Photochemical features of DMPIO and few other phenyl-substituted 2Himidazole 1-oxides were reported experimentally, [7,8] though no similar studies on TMIO have been reported so far to the best of our knowledge. This current study is an attempt to investigate the mechanism behind the photochemistry of this whole class of cyclic nitrones taking TMIO and DMPIO as the two reference systems (Figure 1).…”

Nitroxides with two pK values—useful spin probes for pH monitoring within a broad range

“…The 2,5-dihydro-1H-imidazoles 3a-c were synthesized by condensation of 3-(hydroxyamino)-3-methylbutan-2-one 2 with ammonia and corresponding aldehydes, in a similar way to the procedure for 3a described earlier. 9 A mild oxidation of 3a-c with lead dioxide in methylene chloride yielded 4,4,5trimethyl-4H-imidazole 3-oxides 4a-c. The nitrosation of 4b-c was performed using the i-PrONO-i-PrONa system, while for 4a, a better yield of the 5-hydroximinomethyl derivative 5a was achieved using the i-PrONO-Et 3 N system.…”