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Application of 1H and 13C NMR to the structural elucidation of tetrahydroquinoxalines condensed with five-membered heterocycles

✍ Scribed by V. N. Charushin; A. I. Chernyshev; N. N. Sorokin; O. N. Chupakhin

Publisher: John Wiley and Sons
Year: 1984
Tongue: English
Weight: 425 KB
Volume: 22
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.1270221209

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✦ Synopsis

€I and =C NMR spectral data for 21 N-rnethyltetrahydroquinoxalines annelated with furan, p p l e , imidazole or thiazole rings are reported. Unambiguous assignments of the ring junction =C resonances were made on the basis of selective decoupling experiments and with the aid of one-bond and long-range %-'H coupling constants. The effects of five-membered heterocycles on the 'H and ' % chemical shifts of the rhg junction hydrogen and carbon atoms are considered. Values of one-bond 'J(CH) and vicinal 3 J o coupling constants between the ring junction protons are also discussed as a diagnostic means for structnral elucidation of tetrahydmquinoxalines condensed with five-membered heterocycles. Cyclizations of azines and azinium cations with bifunctional nucleophilic reagents are gaining interest as simple and, therefore, very attractive synthetic routes to a large variety of condensed heterocyclic compound^.'^ In particular, a number of one-step syntheses of tetrahydroquinoxalines condensed with f ~r a n , ~ p y r r ~l e , ~? ~ imidazole' and thiaz~le'~'~ rings have recently been reported. All these fused heterocyclic systems were obtained by cyclizations based on the diaddition reaction of 1,3-dinucleophiles, such as p -diketones, thioureas, thioamides and dithiocarbamates, to N-alkylquinoxalinium salts [Eqn (1)].4-10 ' H AND 13C NMR. TE7TFL4HYDROQUINOXALINlZS CONDENSED WITH 5-MEMBERED HETEROCYCLES

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