Imidazolo-5 ,4 :2,3-quinoxalines,

This nucleus has also been referred to as 4,5-quinoxalinoimidazole and imidazolo-5, 4 2,3-quinoxaline. Most of the reported derivatives of this ring system are cyanine dyestuffs and may be named accordingly. For example, Chemical Abstracts indexes compound SO as an imidazo[4,5-h]quinoxalinocarbocyanine, as well as by using more systematic nomenclature. Similarly 51 may also be called an imidazo[4,5-h]quinoxalino-indocarbocyanine, and compound 52 is referred to as an imidazo[4,5-b ]quinoxalinothiacarbocyanine. 

The di-imine (287), obtained by base-catalysed ring-contraction of (286) (see p. 271), condenses with o-phenylenediamine, giving the imidazolo-quinoxaline (288) in 95% yield (Scheme 113). This is another example of the greater reactivity of imines over carbonyls in the synthesis of 1,4-diazines, as the analogous trioxoimidazole gives a spiro-compound with o-phenylenediamine. ... 

IQ 2-amino-3-methyl imidazo[4,5-/ quinoline nh2 r CH3 MelQx 2-amino-3,8-dimethyl imidazo [4,5-/ quinoxaline nh2 MelQ 2-amino-3,4-dimethyl imidazolOS quinoline nh2 W XH3... 

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... 

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