60418-46-4Relevant academic research and scientific papers
DIMETHYLBENZOPYRAZOLOTRIAZOLE vs METHYLPYRAZOLOQUINOXALINE FROM 3,5-DIMETHYL-1-(2-NITRENOPHENYL)PYRAZOLE
Albini, Angelo,Bettinetti, Gian Franco,Minoli, Giovanna
, p. 331 - 334 (1981)
The chemistry of singlet and triplet 3,5-dimethyl-1-(2-nitrenophenyl)pyrazole is examined.Intramolecular electron transfer is found to play a key role in determining the easy reaction to the ylide (VII) from the singlet state and the "lazyness" of the triplet state.
Role of conformation and electronic structure in the chemistry of ground and excited state o-pyrazolylphenylnitrenes
Carra, Claudio,Bally, Thomas,Albini, Angelo
, p. 5552 - 5562 (2007/10/03)
The chemistry of 2-(1-pyrazolyl)- (2a) and 2-[1-(3,5-dimethylpyrazolyl] phenylnitrene (2b) has been studied in EtOH solution at room temperature, in EtOH glasses at 90 K, and in Ar matrices at 12 K. These nitrenes were chosen as suitable models for clarifying the mechanism of intramolecular reactions because attack at the pyrazole ring can occur according to different modes and the asymmetry of the substituent gives rise to different conformations. Detailed DFT and CASSCF/CASPT2 studies on the conformation and decay paths of both spin states of the nitrenes have been carried out. Ring expansion to dehydroazepines (via benzoazirines) is calculated to be competitive in both nitrenes, but in the dimethyl derivative, 2b, attack onto the N lone pair (which is made more nucleophilic by the methyl groups) is favored. The higher barriers (by 4-8 kcal/mol) in singlet 2a cause 60-70% of this nitrene to decay by intersystem crossing to the triplet. Thus, the seemingly straightforward formation of benzo-fused heterocycles through intramolecular attack of the pyrazoline N lone pair by the singlet phenylnitrene can only overcome ring expansion and intermolecular reactions under favorable circumstances. The comparatively persistent triplet nitrenes are characterized in matrices, and the yields of photocyclization products (mainly pyrazolo[1,5-a]benzimidazole (7) from 2a and 5,6-dihydropyrazolo[1,5-a]quinoxaline (8) from 2b) are shown to depend on the preferred conformation of the starting azide and nitrene.
Photodecomposition of some para-substituted 2-pyrazolylphenyl azides. Substituents affect the phenylnitrene S-T gap more than the barrier to ring expansion
Albini, Angelo,Bettinetti, Gianfranco,Minoli, Giovanna
, p. 3104 - 3113 (2007/10/03)
A series of para-substituted (H, Me, Cl, F, CF3, OMe, NMe2) phenyl azides bearing a dimethylpyrazolyl group in position 2 allowing intramolecular trapping of singlet nitrene have been photolyzed at both 295 and 90 K in ethanol. For t
Reactivity of singlet and triplet arylnitrenes: Temperature-dependent photodecomposition of 1-(2-azidophenyl)-3,5-dimethylpyrazole
Albini, Angelo,Bettinetti, Gianfranco,Minoli, Giovanna
, p. 7308 - 7315 (2007/10/03)
At >200 K photolysis of 1-(2-azidophenyl)-3,5-dimethylpyrazole (5) gives 1,3-dimethylpyrazolobenzotriazole (6, by electrophilic cyclization of singlet nitrene 4) or, in the presence of diethylamine, aminoazepine 8 (by addition of the nucleophile and rearr
Chemistry of Nitrenes Generated by the Photocleavage of Both Azides and a Five-Membered Heterocycle
Albini, A.,Bettinetti, G.,Minoli, G.
, p. 6928 - 6934 (2007/10/02)
Pyrazolobenzotriazole and some of its derivatives (2a-c) are photochemically cleaved to form 2-(1-pyrazolyl)phenylnitrenes, which are also obtained through a more conventional path by photodecomposition of the pyrazolylphenyl azides (1a-c).Product
Competitive Cyclisations of Singlet and Triplet Nitrenes. Part 8. The 1-(2-Nitrenophenyl)pyrazoles and Related Systems
Lindley, John M.,McRobbie, Ian M.,Meth-Cohn, Otto,Suschitzky, Hans
, p. 982 - 994 (2007/10/02)
The title nitrenes, derived by nitro-group deoxygenation with triethyl phosphite or by thermolysis or photolysis of the corresponding azide, have been studied.The effect of substituents (Cl, Br, OMe, NMe2, Me, CF3, and NO2) both meta and para to the nitrene has been examined as a determinant of the preferred mode of cyclisation to either a pyrazolobenzotriazole or a pyrazoloquinoxaline.Similarly, the role of solvents, sensitisers, and quenchers has been studied.Routes to the isomeric 1- and 2-(2-nitrophenyl)-4,5,6,7-tetrahydroindazoles have been defined and the literature corrected by studing the nitrene-mediated cyclisation of these products.The chemistry of the analogous 1-(2-carbenophenyl)- and the 1-(2-nitrenosulphonylphenyl)-3,5-dimethylpyrazoles has also been examined, the former giving 2-(3,5-dimethylpyrazol-1-yl)-benzaldazine and -benzyl alcohol while the latter gave products of intramolecular nitrene attack (a pyrazolobenzothiatriazine) and intermolecular reaction.Rationalisations for all the reaction pathways have been advanced.
