Pyrazolo quinoxalines, formation from

Lindsley and co-workers developed a general procedure towards the collection of diverse heterocyclic scaffolds from common 1,2-diketone intermediates 96. Substituted quinoxalines 97, fused pyrazolo [ 4,5-g ] quinoxalines 98 and imidazolo[3,4-g]quinoxalines 99 as well as pyrido[2,3-fo]pyrazines 100 and Ihicno[3,4-fo Ipyrazincs 101 have been prepared in excellent yields [132] (Scheme 54), employing optimized reaction conditions (microwave heating of equimolar mixtures of 1,2-diketone 96 and diamine components at 160 °C for 5 min in 9 1 MeOH - AcOH). The use of microwave irradiation resulted in reduced reaction times (5 min vs. 2-12 hours), improved yields as well as the suppressed formation of polymeric species a characteristic of traditional... 

When 4-oxo-5-methyl-lH,4,5-dihydro-l,2,5-benzotriazepine is heated with hydrochloric acid, isomerization occurs with the formation of the N-iminoquinoxaline 4. The structure of this product was demonstrated by reaction with diethyl acetylenedicarboxylate which on hydrolysis and methylation gave the pyrazolo[l,5-a]quinoxaline 5, identical with authentic material prepared from the appropriately substituted phenylpyrazole. ... 

Many 1-phenylflavazoles derived from sugars have been characterized by chromatographic Rf values " and by x-ray diffraction patterns. " Most syntheses of pyrazolo[3,4-b]quinoxalines involve polyhydroxy-alkylquinoxalines as intermediates and, by reaction with phenylhydrazine, result in the formation of 1-phenyl substituted derivatives of the ring system. Thus the o-arabotetrahydroxybutyl compound 6, obtained from reaction of o-glucose with o-phenylenediamine, reacts with three moles... 

A study of the scope of this reaction has been performed which shows that excess phenylhydrazine will convert the disubstituted quinoxalines 19 into the pyrazolo[3,4-h]quinoxaline 20. Analogously hydroxylamine gave the isoxazolo compound 21 from these starting materials. The compounds 19 (R = Me or Ph) did not undergo cyclization with phenylhydrazine. A reaction mechanism has been suggested (see Scheme 1) which is analogous to osazone formation in sugar chemistry. 

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