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

We describe the one-pot direct N-acylation of indazole with carboxylic acids using DMAPO/Boc₂O system. This system is simple and provides N1-acyl indazoles in high yield with high N1 selectivities. 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.

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 S_N2 alkylation of indazole.

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