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Expedient Synthesis of Substituted Benzoheterocycles using 2‐Butoxy‐2,3‐dihydrofurans as [4+2] Benzannulation Reagents

Research paper by Changhui Liu, Wenbo Huang, Man Wang, Bin Pan, Yanlong Gu

Indexed on: 10 May '16Published on: 09 May '16Published in: Advanced Synthesis & Catalysis



Abstract

2‐Alkoxy‐2,3‐dihydrofurans were found to be versatile benzannulation reagents. Indoles can be synthesized in good to excellent yields via the [4+2] annulation of 2‐butoxy‐2,3‐dihydrofuran with pyrroles catalyzed by copper bromide. With the same protocol, carbazoles can also be obtained when indoles are used as starting material with the aid of p‐toluenesulfonic acid. This type of benzannulation reagent can also be used to synthesize benzofuran, benzothiophene and naphthalene derivatives in the presence of a catalytic amount of triflic acid in moderate yields. This benzannulation protocol features wide substrate scope and mild reaction condition. Moreover, most of examples have a good regioslectivity.