DMAPO/Boc₂O‐Mediated One‐Pot Direct N1‐Acylation of Indazole with Carboxylic Acids: A Practical Synthesis of N1‐Functionalized Alkyl Indazoles

This report describes the one‐pot direct N ‐acylation of indazole with carboxylic acids using our previously developed 4‐( N , N ‐dimethylamino)pyridine N ‐oxide (DMAPO)/di‐ tert ‐butyl dicarbonate (Boc 2 O) system. This simple system provides N 1‐acyl indazoles in high yield with high N 1 selectivities and does not require the use of activated derivatives of carboxylic acids or high temperatures. This new method exhibits a wide substrate scope (>40 examples). In addition, a new synthesis of N 1‐functionalized alkyl indazoles utilizing N 1‐acyl indazoles as starting materials was achieved. This stepwise protocol is useful for the selective synthesis of structurally diverse N 1‐functionalized alkyl indazoles, which are difficult to synthesize by other methods such as the Mitsunobu reaction and classical S N 2 alkylation of indazole.