- Quinoxalines. Part 12: Synthesis and structural study of 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines - The dehydrogenative cyclization with hydroxylamine hydrochloride
-
Starting with 2-acetylquinoxaline a novel class of heterocyclic compounds, the 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines 4, were prepared by following two different synthetic procedures: 2-acetylquinoxaline reacted with thiosemicarbazide to the thiosemicarbazones 1a which was (i) cyclized with α-halogeno ketones to the thiazoles 3. These compounds were dehydrogenated in acidic medium to the title compounds 4. (ii) The thiosemicarbazone 1a could be also dehydrogenated using NH2OH·HCl to the thioamide 5a and these, finally, were cyclized with α-halogeno ketones to the title compounds 4. Only thiazole 3a was isolated, the other thiazoles 3 were dehydrogenated in a one-pot procedure. From the thioamide 5a also both the compounds 9, by reacting with dibromodiacetyl, and 10, by treatment with dimethyl acetylenedicarboxylate, were obtained. The analysis of both the 1H and 13C NMR spectra was not straightforward but could be attained finally by employing the whole arsenal of 1D and 2D NMR spectroscopy.
- Sarodnick, Gerhard,Heydenreich, Matthias,Linker, Torsten,Kleinpeter, Erich
-
-
Read Online
- Unequivocal determination of isomeric products of reaction between 3- methyl-1-phenyl-2-pyrazoline-4,5-dione and aromatic 1,2-diamines
-
Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5- dione with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]quinoxaline products are distinguished by comparison of their 2D z-gradient selected 1H,15N HMBC (Heteronuclear Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is recognizable by the cross-peak for CH3(3)-N4 and H5-N4 interactions, indicates substitution in position 6 or 7. The applied method is expected to be useful for structure determinations in other positional isomers.
- Kolehmainen, Erkki,Kucybala, Zdzislaw,Gawinecki, Ryszard,Paczkowski, Jerzy,Kacala, Anna
-
-
Read Online
- A new regiospecific synthesis method of 1H-pyrazolo[3,4-b]quinoxalines – Potential materials for organic optoelectronic devices, and a revision of an old scheme
-
A series of 6-substituted-1,3-diphenyl-1H-pyrazolo[3,4-b]quinoxalines were prepared using a new synthetic pathway: reductive cyclization of appropriate 5-(o-nitrophenyl)-pyrazoles with ferrous oxalate or triphenylphosphine. The main advantage of this procedure is that, contrary to the older protocols of pyrazolo[3,4-b]quinoxaline synthesis, this method allows for a substituent to be introduced to the carbocyclic ring without the formation of isomers. The pyrazole ring can also be modified to some extent. Furthermore, we propose a new mechanism for the oldest reported pyrazolo[3,4-b]quinoxaline synthesis, based on the condensation between o-phenylenediamine and 3,4-pyrazolin-5-diones.
- Danel, Andrzej,Wojtasik, Katarzyna,Szlachcic, Pawe?,Gryl, Marlena,Stadnicka, Katarzyna
-
p. 5072 - 5081
(2017/07/28)
-
- New synthesis of pyrazolo[3,4-b][1,4,5]benzothiadiazepine, -[1,4,5]benzoxadiazepine, -[1,4,5]benzotriazepine and pyrazolo[3,4-b]quinoxaline derivatives
-
New pyrazolo[3,4-b][1,4,5]benzothiadiazepine and its analogues 3 have been obtained by reaction of 4-nitrosopyrazoles 1 with 2-aminothiophenol 2a and its analogues 2b,c. Under fused conditions, dipyrazolyl derivatives 7a was obtained with a trace amount of quinoxaline 5a. On the other hand, 5b and 7b were obtained in equal amounts. A proposed pathway is presented.
- El-Rady, Eman A.
-
p. 859 - 862
(2007/10/03)
-
- Quinoxalines X [1]. A new and convenient synthesis of 1H-pyrazolo[3,4-b]quinoxalines (flavazoles)
-
Quinoxaline-2-aldoximes and -ketoximes (6) react with hydrazine, alkylhydrazines or arylhydrazines under acidic conditions to afford 1H-pyrazolo[3,4-b]quinoxalines (flavazoles) (1). Since the oximes (6) are easily available from phenylenediamine, the herein described methodology provides a convenient two step entry to various functionalized flavazoles. Furthermore, acylation and alkylation of the 1-unsubstituted 1H-pyrazolo[3,4-b]quinoxalines 7 proceeds smoothly and in good yield to afford 31 different flavazoles 11 and 12.
- Sarodnick,Linker
-
p. 829 - 836
(2007/10/03)
-
- Development of new dyeing photoinitiators for free radical polymerization based on the 1H-pyrazolo[3,4-b]quinoxaline skeleton. Part 2
-
Several dyes containing a pyrazoloquinoxaline moiety have been synthesized and evaluated as novel photoinitiators for free radical polymerization induced with the argon-ion laser. The kinetic study of photoinitiated polymerization, performed for viscous monomeric formulations with the use of the most effective dye-N-phenylglycine derivative photoinitiating systems has shown unusual kinetic properties. The experimental data show the presence of "Marcus inverted region"-like kinetic behavior. Analysis of possible reasons for this specific feature suggests that one of the processes that may be responsible for such a specific property is the back electron transfer process. Study of photo-initiated polymerization has shown that there is a linear relationship between the rate of polymerization and the square root of the efficiency of singlet oxygen formation. This finding clearly indicates that the electron transfer process between the tested dyes and electron donors occurs via a triplet state. The observed relationship is also in good agreement with the general equation describing the rate of polymerization, which is (among other parameters) a function of the square root of the quantum yield of triplet state formation. In the paper, it is also shown that the structure of the dye has a strong effect on its polymerization photoinitiation ability. The dyes tested were prepared in such a way as to, (i) restrict the rotational freedom of selected parts of the molecule and (ii) increase the quantum yield of the triplet state formation. The latter was achieved by introducing to the molecule a heavy atom (ZCl2, CI) or different heavy atoms (CICl2).
- Kucybala, Zdzislaw,Pyszka, Ilona,Paczkowski, Jerzy
-
p. 1559 - 1567
(2007/10/03)
-
- Reactivity of 3-methyl-1-phenyl-2-pyrazoline-4,5-dione with amines
-
Reaction of 3-methyl-1-phenyl-2-pyrazoline-4,5-dione (1) with amine or diamine derivatives has been investigated.Primary aliphatic amines or diamines with α-hydrogens react with 1 to give rubazonic acid (7), while 1 with amines substituted in α-position addition products are formed which yield Schiff bases an heating.Aromatic o-diamines react with 1 to give different heterocyclic derivatives.
- Metwally, Saoud A. M.,Atta, Ferial M.,El-Monem, Maisa E. Abd
-
p. 248 - 250
(2007/10/02)
-
- Synthesis and Biological Activity of Pyrazoloquinoxaline Dimethine Cyanine Dyes
-
New asymmetrical dimethine cyanines (VIa-f) and their bases (VIIa,b), incorporating pyrazoloquinoxaline moiety or its ethiodide, have been prepared and tested for their antibacterial and fungicidal activities.
- El-Maghraby, M. A.,Koraiem, A. I. M.,Khalil, Z. H.,El-Hamed, R. M. Abu
-
-