Regioselective Protection At N-2 And Derivatization At C-3 Of Indazoles

Indazoles are regioselectively protected at N-2 by a 2-(tri-methylsilyl) ethoxymethyl (SEM) group using novel conditions. The SEM group can efficiently direct regioselective C-3 lithiation, and the resulting nucleophile can react with a wide range of electrophiles to generate novel indazole derivatives. The SEM group can be removed by treatment with TBAF in THF or aqueous HCl in EtOH.