Synthesis of 5-aryl-3,3′-bis-indolyl and bis-7-aza-indolyl methanone derivatives from 5-bromo-7-azaindoles via sequential methylenation using microwave irradiation, CAN oxidation, and Suzuki coupling reactions

A catalyst-free and green chemical method has been developed for the methylenation of indole and N-methyl-7-aza indoles with aqueous formaldehyde afforded respective N,N '-dimethyl-3,3 '-bis-7-azaindolylmethanes under microwave irradiation in excellent yield. Subsequent oxidation of the products thus obtained, using one electron chemical oxidant CAN afforded N,N '-dimethyl-3,3 '-bis-7-azaindolylmethanone derivatives in excellent yield. This resulted in methanone derivatives with halogen substitution at the aryl ring which when subjected to Suzuki coupling with aryl boronic acids furnished highly functionalized fluorescent biaryl derivatives. Plausible mechanisms, characterization including XRD, and evaluation of photophysical properties of the Suzuki coupled products are described.

Automated summary

A catalyst-free and green chemical method was developed for the methylenation of indole and N-methyl-7-aza indoles using aqueous formaldehyde. Under microwave irradiation, high yields of respective N,N'-dimethyl-3,3'-bis-7-azaindolylmethanes were obtained. The subsequent oxidation of the products resulted in N,N'-dimethyl-3,3'-bis-7-azaindolylmethanone derivatives in excellent yield. These derivatives, with halogen substitution at the aryl ring, were used in Suzuki coupling reactions to produce highly functionalized fluorescent biaryl derivatives.