Highly Efficient Synthesis of 1H-Indazole-3-carboxylic Acid Derivatives via Diazotization Reaction

Direct conversion of ortho-aminobenzacetamides and ortho-aminobenzacetates to the corresponding 1H-indazole-3-carboxylic acid derivatives under the action of diazotization reagents was reported. This method features operational simplicity, mild reaction conditions, rapid reaction rates, high yields, wide substrate scope, offering an efficient and concise route to synthesis of 1H-indazole-3-carboxylic acid derivatives. The drugs granisetron and lonidamine were synthesized successfully using this protocol with 46% and 60% total yields, respectively. Preliminary mechanistic study suggests that diazonium salt is a key intermediate.