A c c l e r a t e d S y n t h e s i s o f 1 , 2 , 4 -T r i a z i n o [ 5 , 6 -b ] i n d o l e -3 -t h i o l s a n d b y M i r c r o w a v e I r r a d i a t i o n Abstract : Microwave irradiation has been used to accelerate the conversion of isatin (1), 5-chloroisatin (2), and N-benzylisatin (3) to their thiosemicarbazones and their subsequent cyclization into 1,2,4-triazino[5,6-b]indole-3-thiols 7 and 8; and the N-benzyl derivative 9. Selective and complete alkylation of 1, 7, 8, and 9 has also been achieved under microwave irradiation.
The transformation of 2‐chloro‐3‐[5‐(acetoxymethyl)‐1‐phenylpyrazol‐3‐yl]quinoxaline 3 to 1‐aryl‐4‐[5‐(hydroxymethyl‐1‐phenylpyrazol‐3‐yl][1,2,4]triazolo[4,3‐a]quinoxalines 4a‐c has been achieved upon treatment with aroylhydrazines in boiling butanol. Compounds 4a‐c were smoothly acetylated by acetic anhydride to give their acetyl derivatives 5a‐c in good yield. 4‐[5‐(Acetoxymethyl)‐1‐phenylpyrazol‐3‐yl]‐1‐methyl[1,2,4]triazolo[4,3‐a]quinoxaline was prepared by ring closure of 2‐hydrazino‐3‐[5‐(hydroxymethyl)‐1‐phenylpyrazol‐3‐yl]quinoxaline 6 by the action of acetic anhydride. The reaction of 6 with acetylacetone afforded 3‐[5‐(hydroxymethyl)‐1‐phenylpyrazol‐3‐yl]‐2‐(3,5‐dimethylpyrazol‐1‐yl)quinoxaline 8. In addition, the reaction of 3 with sodium azide in boiling N, N‐dimethylformamide yielded the fused tetrazolo[1,5‐a]quinoxaline 9.
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