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

Abstract

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 (Boc2O) system. This simple system provides N1‐acyl indazoles in high yield with high N1 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 N1‐functionalized alkyl indazoles utilizing N1‐acyl indazoles as starting materials was achieved. This stepwise protocol is useful for the selective synthesis of structurally diverse N1‐functionalized alkyl indazoles, which are difficult to synthesize by other methods such as the Mitsunobu reaction and classical SN2 alkylation of indazole.