Arene Diazonium Tetrafluoroborate Salts: Novel Lewis Acid Catalysts for Friedel-Crafts Alkylation of Indoles with α,β-Unsaturated Ketones

In this study, the Friedel crafts alkylation of indole with alpha, beta-unsaturated ketones catalyzed by arene diazonium tetrafluoroborate salts is reported for the first time, and the optimal conditions of this reaction were explored. The experimental results show that the optimal conditions employed 10 mol % 2-(2-bromophenoxy)phenyl diazonium fluoborate (2) as a catalyst, CH3OH as a solvent, 60 degrees C as reaction temperature, and 24 h as reaction time. Under these optimized conditions, the reaction of indoles with various alpha,beta-unsaturated ketones can proceed smoothly to obtain aimed products (8). Yields of these reactions ranged from 60 % to 92 %. The reaction conditions are mild and the reaction operation is simple.

Automated summary

This study reports the first Friedel- Crafts alkylation of indole with alpha, beta-unsaturated ketones catalyzed by arene diazonium tetrafluoroborate salts, and explores the optimal conditions of the reaction. The experimental results show that the optimal conditions include using 10 mol% of 2-(2-bromophenoxy)phenyl diazonium fluoride borate (2) as the catalyst, CH3OH as the solvent, 60 degrees C as the reaction temperature, and 24 hours as the reaction time. Under these optimized conditions, the reaction of indoles with various alpha, beta-unsaturated ketones can proceed smoothly to obtain the intended products (8), with yields ranging from 60% to 92%. The reaction conditions are mild and the reaction operation is simple.