Direct Synthesis of Benzo[f]indazoles from Sulfonyl Hydrazines and 1,3-Enynes by Copper-Catalyzed Annulation

Abstract

A novel and efficient strategy for the direct synthesis of benzo[f ]indazoles via copper-catalyzed cascade reaction of sulfonyl hydrazides with 1,3-enynes under mild conditions has been developed. This method achieves the formation of two C−N bonds and one C−C bond in one pot, providing a series of benzo[f ]indazoles in moderate to good yields with good functional group tolerance and remarkable regioselectivity.

Sulfonyl Hydrazides in Organic Synthesis: A Review of Recent Studies

“…69‐1). In 2019, Wang and co‐workers utilized a copper catalyst in the dicyclization of 1,3‐enynes with sulfonyl hydrazides in the synthesis of benzo[ f ]indazoles (Eq. 69‐2).…”

Regioselective Synthesis of 2,3‐Dihydrobenzo[f]isoindolones via Ag‐Catalyzed Sequential Ugi 4CR/Cascade Radical Cyclization Reaction

“…Based on the control experiment results and previous literature survey, [18,21‐23] a plausible mechanism is proposed in Scheme 3. Initially, under the action of Cs 2 CO 3 , the peptidyl position which has an acidic character could be deprotonation to form the carbanion 7 .…”

“…On the other hand, 1,3‐enynes are among the most versatile synthetic handles in chemistry, and have been widely used for the assembly of elaborate compounds in a highly efficient fashion through synergistic cascade processes [17] . However, because of the intricacies of controlling reaction reactivity, regio‐ and chemo‐selectivity, the cascade radical cyclization of 1,3‐enynes remains a challenging task [18] . Continuing our interest in the development of new strategies for the synthesis of heterocyclic compounds, we herein disclose the first successful construction of a series of 2,3‐dihydrobenzo[ f ]isoindolones by Ag‐catalyzed Ugi 4CR/cascade radical cyclization sequence (Scheme 1d).…”

Synthesis of Fused or Spiro Polyheterocyclic Compounds via the Dehydrogenative Annulation Reactions of 2-Arylindazoles with Maleimides

“…Indazole is not only a key scaffold of many natural products but also an essential unit of a number of synthetic compounds possessing a wide spectrum of pharmaceutical activities including anticancer, antiviral, antidepressant, and anti-inflammatory (Figure ). , In addition, indazole-related conjugated systems are of great interest in biological, chemical, and material sciences. , Despite their importance, reliable methods for the synthesis of indazole-related polyheterocycles (PHCs) are rather limited, and some of them still suffer from the use of highly functionalized substrates, the production of a large amount of waste, and low atom economy. On the other hand, maleimide derivatives are well known for their unique photophysical properties and potent pharmaceutical activities (Figure ).…”