Concise synthesis of bis(indol-3-yl)methane derivatives

This article establishes a novel synthetic method utilizing N-methylindole (1) and enamine ketones (2) as starting materials. The oxidation is facilitated by di(trifluoroacetoxy)iodobenzene (PIFA), with anhydrous copper acetate serving as the catalyst. The reaction proceeds under reflux in toluene for 3 hours, resulting in a three-component "one-pot" synthesis of functionalized bis(indole-3-yl)methane derivatives (3,3'-BIMs) (3). This methodology capitalizes on the electrophilic character of the double bond (enamine ketones 2), enabling it to undergo a Michael reaction with one molecule of indole derivatives 1. Following this, the resulting intermediates are oxidized by PIFA, which promotes the elimination of the aniline group from the enamine ketone, yielding α, β-unsaturated ketones. These α, β-unsaturated ketones subsequently engage in a second Michael reaction with another indole derivatives 1, culminating in the formation of 3,3'-BIMs. The synthesized products were characterized through ¹H NMR, ¹³C NMR, and HRMS analyses. This research highlights the method's advantages, including the accessibility of starting materials, ease of operation, and a streamlined synthetic route, thereby providing a promising approach for the synthesis and screening of bis(indole-3-yl)methane derivatives with potential biological activities.