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. 2021 Jun 28;11(37):22710–22714. doi: 10.1039/d1ra04056a

Cyclization of arylhydrazone 3a to indazoles 4a and 5a.

graphic file with name d1ra04056a-u2.jpg
Entry Reagent Solvent Temp., time Product Yield
1 5 equiv. TFA DCM 25 °C, 12 h 4a 63%
2 5 equiv. TFA MeCN 25 °C, 12 h 4a 64%
3 AcOH Neat r. t., 12 h 4a 0%
4 30 equiv. AcOH MeCN 70 °C, 12 h 4a 56%
5 30 equiv HCOOH MeCN r. t., 12 h 4a 56%
6 3 equiv. K2CO3 MeOH 70 °C, 1 h 5a 67%
7 3 equiv. K2CO3 MeOH 25 °C, 12 h 5a 67%
8 4 equiv. KOH EtOH r. t., 12 h 5a 59%