Sc(III)-Catalyzed Synthesis of Cyclopenta[b]indoles

Sc(III)-Catalyzed Synthesis of Cyclopenta[b]indoles

Author: ChemistryViews

Cyclopenta[b]indoles are indole-fused tricyclic rings. This structure is often found, e.g., in bioactive compounds. Methods for the synthesis of cyclopenta[b]indoles are, thus, interesting research targets. They can, for example, be prepared via annulation reactions using noble metal catalysts. Using lower-cost metals could be useful in this context.

Cheng-Yu He, Wen-Dao Chu, Quan-Zhong Liu, China West Normal University, Nanchong, and colleagues have developed a cycloaddition of vinyl diazoacetates with sulfonyl indoles catalyzed by low-cost Sc(OTf)3 that gives cyclopenta[b]indoles (general product structure pictured). The team reacted different sulfonyl indoles that bear aryl substituents adjacent to the sulfonyl group with vinyl diazoacetates or β-methyl-substituted vinyl diazoacetates, using Sc(OTf)3 as the catalyst, LiBr as an additive, and CHCl3 as the solvent. The reactions were performed at 50 °C in the presence of a molecular sieve under an argon atmosphere.

The researchers obtained the desired cyclopenta[b]indoles in moderate to high yields. They propose that the reaction proceeds via indole-derived α,β-unsaturated imines that are generated from the sulfonyl indoles via the elimination of PhSO2H.


Leave a Reply

Kindly review our community guidelines before leaving a comment.

Your email address will not be published. Required fields are marked *