An improved microwave assisted protocol for Yonemitsu-type trimolecular condensation

Due to the presence of the indole ring in a number of bioactive compounds, novel methods for the preparation of polyfunctionalized indole derivatives are of great interest. The combined use of Lewis acid catalysis and microwave irradiation furnished satisfactory results in the Yonemitsu-type trimolecular condensation of indoles with aldehydes and 1,3-dicarbonyl compounds, such as malonates and acetoacetates. The main advantage of this procedure is the use of a catalytic amount of the Lewis acid and reduction in reaction time. The one pot procedure avoids the isolation and purification of intermediates, thus making the process more environmentally sustainable. The protocol has also been successfully applied to the preparation of novel indole-coumarin derivatives of potential biological interest.