The synthesis of the title compounds is described. Reaction of 1-substituted 2-pyrazolin-5-ones with 5-chloro-1-phenyl-1H-pyrazole-4-carbonyl chloride or 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbonyl chloride, respectively, using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-heteroaroylpyrazol-5-ols, which were cyclized into 1H-pyrano[2,3-c:6,5-c]dipyrazol-4(7H)-ones by treatment with K2CO3/DMF. The latter were converted into the corresponding thiones upon reaction with Lawesson’s reagent. Detailed NMR spectroscopic investigations (1H, 13C, 15N) of the ring systems and their precursors are presented.

Derivatives of the hitherto unknown ring system, pyrazolo[4′,3′:5,6]pyrano[2,3‐b]quinoxalin‐4(1H)‐one, are synthesized in one step from the corresponding 1‐substuituted or 1,3‐disubstituted 2‐pyrazolin‐5‐ones and 3‐chloroquinoxaline‐2‐carbonyl chloride using calcium hydroxide in boiling 1,4‐dioxane. The parent system carrying no substituent in positions 1 and 3 is obtained upon treatment of the 1‐PMB (p‐methoxybenzyl) protected congener with trifluoroacetic acid. Detailed NMR spectroscopic investigations including unambiguous chemical shift assignments of all 1H, 13C, and 15N resonances of the obtained tetracycles are reported.

NMR spectroscopic studies are undertaken with derivatives of 2-pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts ((1)H, (13)C, (15)N) and coupling constants ((1)H,(1)H; (13)C,(1)H; (15)N,(1)H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of (13)C,(1)H spin coupling constants is accomplished by 2D (delta,J) long-range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3-hydroxy-2-pyrazinecarboxylic acid are discussed.

Pyrazine derivatives R 0550Pyrazolo [4',3':5,6]pyrano[2,3-b]quinoxalin-4(1H)-one: Synthesis and Characterization of a Novel Tetracyclic Ring System. -(ELLER*, G. A.; DATTERL, B.; HOLZER, W.; J.

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