A new method for the synthesis of novel 6‐quinoxalinylpyrazolo[5,1‐c][1,2,4]triazines

The reaction of the quinoxaline 1 with 4‐ethoxycarbonyl‐1 H ‐pyrazole‐5‐diazonium chloride 7 at room temperature gave 3‐[α‐(4‐ethoxycarbonyl‐1 H ‐pyrazol‐5‐ylhydrazono)methoxycarbonylmethyl]‐2‐oxo‐1,2‐dihydroquinoxaline 8. The pmr spectrum of 8 in deuteriodimethylsulfoxide supported the presence of two tautomers 8‐I and 8‐II. Refluxing of 8 in N,N ‐dimethylformamide or acetic acid resulted in cyclization to afford 8‐ethoxycarbonyl‐4‐oxo‐3‐(3‐oxo‐3,4‐dihydroquinoxalin‐2‐yl)‐1,4‐dihydropyrazolo[5,1‐ c ][1,2,4]triazine 9. Compound 9 was also obtained directly by the reaction of 1 with 7 under reflux in better yield. The reaction of 9 with hydrazine hydrate provided the hydrazinium salt 10 , while the reactions of 9 with triethyl and trimethyl orthoformates in the presence of 1,8‐diazabicyclo[5,4,0]‐7‐undecene produced 8‐ethoxycarbonyl‐4‐ethoxyl‐3‐(3‐oxo‐3,4‐dihydroquinoxalin‐2‐yl)pyrazolo[5,1‐ c ][1,2,4]triazine 11a and 8‐ethoxycarbonyl‐4‐methoxyl‐3‐(3‐oxo‐3,4‐dihydroquinoxalin‐2‐yl)pyrazolo[5,1‐ c ][1,2,4]triazine 11b , respectively. The chlorination of 11a with phosphoryl chloride gave 3‐(3‐chloroquinoxalin‐2‐yl)‐8‐ethoxycarbonyl‐4‐ethoxylpyrazolo[5,1‐ c ]‐[1,2,4]triazine 12 , whose reaction with morpholine afforded 8‐ethoxycarbonyl‐4‐ethoxyl‐3‐[3‐(morpholin‐4‐yl)‐quinoxalin‐2‐yl]pyrazolo[5,1‐ c ][1,2,4]triazine 13.