Synthesis of indazolones
The use of blocked (masked) N-isocyanate precursors enables the formation of indazolones by Friedel-Crafts cyclization. Substrate synthesis has also been improved using a copper-catalyzed arylation of phenyl carbazates with pentavalent bismuth reagents that is compatible with the hemilabile OPh blocking group.
E. B. Elkaeed, J. An, A. M. Beauchemin, J. Org. Chem., 2017, 82, 9890-9897.
The key step in a concise, one-step route to indazolones from primary alkyl amines and o-nitrobenzyl alcohols involves base-mediated in situ o-nitrobenzyl alcohol → o-nitrosobenzaldehyde conversion.
J. S. Zhu, N. Kraemer, M. E: Shatskikh, C. J. Li, J.-H. Son, M. H. Haddadin, D. J. Tantillo, M. J. Kurth, Org. Lett., 2018, 20, 4736-4739.