Tautomeric Behaviors of 3-(1,3,4-Oxadiazol-2-yl)methylene-2-oxo-1,2,3,4-tetrahydroquinoxalines
1983; Elsevier BV; Volume: 20; Issue: 10 Linguagem: Inglês
10.3987/r-1983-10-1917
ISSN1881-0942
AutoresYoshihisa Kurasawa, Atsushi Takada,
Tópico(s)Synthesis and Reactions of Organic Compounds
Resumo3-(1,3,4-Oxadiazol-2-y1)methylene-2-0x0-l,2,3,4tetrahydroquinoxalines ( : a, ! ) were found to exhibit the two tautomers in dimethylsulfoxide and three tautomers in trifluoroacetic acid, and their tautomeric species were assumed based on the NMR and UV spectral data.Tautomeric equilibria of 3-methoxycarbonylmethylene-Z-oxo-1,2,3,4-tetrahydroquinoxa- line (la) and related compounds (lb-e) have been investigated with NMR and UV spec-----troscopy by Mondelli and Mer1ini.lThat is, the NMR spectra in dimethylsulfoxide (DMSO) demonstrated that two tautomers A and B coexisted in la,b,c, and the tautomer ---" A was predominant in ld,e, as shown in Scheme 1 and Table I.Moreover, the NMR spec---tra in trifluoroacetic acid (TFA) clarified that 1a.b existed as the tautomer B, and --lc,d,e as the tautomer A. Thus the above compounds la-e predominate in only one tau---" ---tomer A or B in TFA.To the contrary, 3-(1,3,4-oxadiazol-2-yl)methylene-2-oxo-l,Z; 3,4-tetrahydroquinoxaline (Za) and 3-(5-methyl-1,3,4-oxadiazol-2-yl)methylene-Z-oxo-" -1,2,3,4-tetrahydroquinaxaline (Zb) (Scheme Z), previously prepared by us,' displayed -
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