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Kurasawa, Yoshihisa,Hosaka, Tomoyoshi,Takada, Atsushi,Kim, Ho Sik,Okamoto, Yoshihisa 대구효성가톨릭대학교 자연과학연구소 1994 基礎科學硏究論集 Vol.1994 No.1
The 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1a-e and 2a-ishowed tautomeric equilib-ria between the hydrazone imine A and diazenyl enamine B forms in dimethyl sulfoxide media. The sub-stituent effects on the tautomer ratios of A to B in compounds 1a-e and 2a-i were studied by the nmr spec-troscopy. The electron-donating or electron-withdrawing p-substituents R^1 in compounds 2a-i representeda tendency to increase the ratios of the tautomer A or the tautomer B. respectively, exhibiting the linearcorrelation of the Hammett constants δ_p (-0.17 to +078) with the tautomer ratios of A to B or the tau-tomeric equilibrium constants K_T. However, the presence of the ester group R^2 in compounds 1a-e induced the exclusive existence of the tautomer A regardless of the nature of the p-substituent R^1. In the tautomeric thermodynamic study, the elevating temperature increased the ratios of the hydrazone imine tautomer A in compounds 2a-i. The tautomeric thermodynamic parameters △G˚, △H˚ and △S˚were derived from the van't Hoff plots for compounds 2a,b,h,i, wherein the entropy term dominated the free-energy difference between the A and B tautomers.
Kurasawa, Yoshihisa,Kureyama, Tomomi,Yoshishiba, Noriko,Kathoh, Ritsuko,Takada, Atsushi,Kim, Ho Sik,Okamoto, Yoshihisa 대구효성가톨릭대학교 자연과학연구소 1993 基礎科學硏究論集 Vol.1993 No.1
The reaction of 6-chloro-2-(l-methylhydrazino)quinoxaline 4-oxide 8 with furfural, 3-methyl-2-thiophene-carbaldehyde, 2-pyrrolecarbaldehyde, 4-pyridinecarbaldehyde and pyridoxal hydrochloride gave 6-chloro-2-[2-(2-furylmethylene)-l-methylhydrazino]quinoxaline 4-oxide 5a, 6-chloro-2-[1-methyl-2-(3-methyl-2-thienyl-methylene)hydrazino]quinoxaline 4-oxide 5b, 6-chloro-2-[1-methyl-2-(2-pyrrolylmethylene)hydrazino]quinoxaline 4-oxide 5c, 6-chloro-2-[1-methyl-2-(4-pyridylmethylene)hydrazino]qunoxaline 4-oxide 5d and 6-chloro-2-[2-(3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridylmethylene)-1-methylhydrazino]quinoxaline 4-oxide 5e, respectively. The reaction of compound 5a or 5b with 2-chloroacrylonitrile afforded 8-chloro-3-(2-furyl)-4-hydroxy-1-methyl-2,3-dihydro-1H-1,2-diazepino[3,4-b]quinoxaline-5-carbonitrile 6b, respectively, while the reaction of compound 5e with 2-chloroacrylonitrile furnished 11-chloro-7,13-dihydro-4-hydroxy-methyl-5,14-methano-1,7-dimethyl-16-oxopyrido[3',4':9,8][1,5,6]oxadiazonino[3,4-b]quinoxaline 7.
Tautomeric Structure of 1-Methyldihydropyridazino[3,4-b]quinoxalines in Solution
Kurasawa, Yoshihisa,Takada, Atsushi,Kim, Ho Sik,Okamoto, Yoshihisa 대구효성가톨릭대학교 자연과학연구소 1993 基礎科學硏究論集 Vol.1993 No.1
The reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 1 with ethyl 2-ethoxymethylene-2-cyano-acetate or ethoxymethylenemalononitrile gave 6-chloro-2-[2-{2-cyano-2-ethoxycarbonylvinyl)-1-methylhy-drazino]quinoxaline 4-oxide 3a or 6-chloro-2-[2-(2,2-dicyanovinyl)-1-methylhydrazino]quinoxaline 3b, respec-tively. The reaction of 3a with a base afforded 7-chloro-1-methyl-1,5-dihydropyridazino[3,4-b]quinoxaline 4. From the NOE spectral data, the 1-methyldihydropyridazino[3,4-b]quinoxalines 2a,2b and 4 were found to exist as the 1,5-dihydro from in a dimethyl sulfoxide or trifluoroacetic acid/dimethyl sulfoxide solution.
Kurasawa, Yoshihisa,Kureyama, Tomomi,Yoshishiba, Noriko,Okano, Tomoko,Takada, Atsushi,Kim, Ho Sik,Okamoto, Yoshihisa 대구효성가톨릭대학교 자연과학연구소 1993 基礎科學硏究論集 Vol.1993 No.1
The reaction of 7-chlorotetrazolo[1,5-a]quinoxaline 50oxide 4a or 7-chloro-1,2,4-triazolo[4,3-a]quinoxaline 5-oxide 4b with 2-chloroacrylonitrile gave 7-chloro-4-(2-cyano-2-hydroxyvinyl)tetrazole[1,5-a]quinoxaline 5a or 7-chloro-4-(2-cyano-2-hydroxyvinyl)-1,2,4-triazolo[4,3-a]uinoxaline 5b, respectively. Alcoholysis of com-pound 5a or 5b afforded 7-chloro-4-ethoxycarbonylmethylene-4,5-dihydrotetrazolo[1,5-a]quinoxaline 6a or 7-chloro-4-ethoxycarbonylmethylene-4,5-dihydro-1.2.4-triazolo[4,3-a]quinoxaline 6b, respectively. Compounds 5a,b were found to exist as a syn and anti mixture of the enol form, while compounds 6a,b occurred as the enamine and methylene imine forms. The tautomeric character and/or D-H exchange of the vinyl protons are described for compounds 5a,b and 6a,b.
Yoshihisa, Kurasawa,Kim, Ho Sik,Ritsuko, Katoh,Tae, Kawano,Atsushi, Takada,Yoshihisa, Okamoto 대구효성가톨릭대학교 자연과학연구소 1991 基礎科學硏究論集 Vol.1991 No.1
The reaction of the hydrazones 5a-c with 2-chloroacrylonitrile produced the 1,2-diazepino[3,4-b]quinoxaline hydrochlorides 6a-c, which were transformed into the 5,6,7,13-tetrahydro-5,14-methano-16-oxo-1,5,6-benzoxadiazonino[3,4-b]quinoxalines 7a-c, respectively. The oxidation of 7a-c with diethyl azodicarboxylate afforded the 7,13-dihydro-5,14-methano-16-oxo-1,5,6-benzoxadiazonino[3,4-b]quinoxalines 8a-c, respectively. Compounds 7a-c and 8a-c were also obtained by a one-pot synthesis from 5a-c and 6a-c, respectively.
Synthesis of Mesoionic Triazolo[4,3-α]quinoxalines
Yoshihisa, Kurasawa,Tae, Kawano,Ritsuko, Katoh,Atsushi, Takada,Kim, Ho Sik,Yoshihisa, Okamoto 대구효성가톨릭대학교 자연과학연구소 1992 基礎科學硏究論集 Vol.1992 No.1
The reaction of 6-chloro-2(1-methylhydrazino)quinoxaline 4-oxide 1 or 6-chloro-2-(1-methylhydrazino)-quinoxaline 5 with phenyl isothiocyanate under reflux in N,N-dimethylformamide gave 7-choloro-3-methyl-1,2,4-triazolo[4,3-a]quinoxalin-3-ium-1-thioate 4, which was also obtained by refluxing of 6-chloro-2-[1-methyl-2-(N-phenylthiocarbamoyl)hydrazino]quinoxaline 4-oxide 2b or 6-chloro-2-[1-methyl-2-(N-phenylthiocarbamoyl)hydrazino]quinoxaline 6 in N,N-dimethylformamide.
Kurasawa, Yoshihisa,Hosaka, Tomoyoshi,Ikeda, Kazue,Matsumoto, Yuko,Ishikura, Aiko,Takada, Atsushi,Kim, Ho Sik,Okamoto, Yoshihisa 대구효성가톨릭대학교 자연과학연구소 1994 基礎科學硏究論集 Vol.1994 No.1
The 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 9-11 were synthesized by the reaction of the quinoxalines 6-8 with various p-substituted benzenediazonium salts. Compounds 9-11 showed the tau-tomeric equilibria between the hydrazone imine A and diazenyl enamine B forms in dimethyl sulfoxide media. The substituent effect on the tautomer ratios of A to B was studied by the nmr spectroscopy to clar-ify that the presence of the ester group R^2 on the hydrazone carbon and electron-donating p-substituent R^1 on the side chain benzene ring exhibited a tendency to increase the ratios of the tautomer A.