Pyrazino cinnoline

AMI calculations have been performed on pyrazino[2.3-c]pyridazine and its N-protonated species.2 Energy levels and charge densities were calculated by Hiickel MO calculations.3 MNDO calculations have also been performed on a benzo-annulated pyrazino[2,3-c]pyridazine (quinoxalino[2,3-c]cinnoline).69... 

Cyclization of /V- [2-(2-nitrobenzylidene)amino]phenyl acetamides 3 with potassium cyanide in methanol leads to quinoxalino[2,3-c]cinnolines 5 which also contain the pyrazino[2,3-c]-pyridazine skeleton. The reaction is supposed to proceed via the addition of hydrogen cyanide to the N —C double bond (formation of 4) followed by formation of the quinoxaline ring and finally closing of the pyridazine ring. The yields obtained are up to 62%.78... 

Halogenation reactions are known for quinoxalino[2,3-c]cinnolines (3,4- and 6,7-bisbenzo-an-nulatcd pyrazino[2,3-c]pyridazines)69 and for pyridazino[3,4-6]quinoxalines (6,7-benzo-annu-lated pyrazino[2,3-c]pyridazines).77... 

Note. Cinnolinamines and their derivatives have been used widely as substrates for further cyclocondensations. Some typical examples are given here. 3,4-Cinnohnediamine (38) with glyoxal gave pyrazino[2,3-c]cinnoline (39) (H2O, 100°C, 15 min 71%). °... 

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