Grieco three-component coupling
The Grieco three-component coupling is a multicomponent organic reaction describing synthesis of nitrogen-containing six-member heterocycles from aldehydes, anilines, and electron-rich olefins. The reaction is catalyzed by trifluoroacetic acid or Lewis acids such as ytterbium trifluoromethanesulfonate (Yb(OTf)3). The reaction is first reported by,[1][2] and named after American organic chemist Paul Grieco.
The mechanism of the Grieco three-component reaction involves the formation of the immonium ion intermediate and an aza-Diels-Alder reaction between the electro-rich olefin and the immonium ion. Unlike imines which usually functions as dienophile, the immonium ion derived from aryl amines and aldehydes functions as aza-diene and can react with olefins through a [4+2] Diels-Alder reaction mechanism.
Researchers have extended the Greico three-component reaction to reactants or catalysts immobilized on solid support, which greatly expands the application of this reaction to various combinatorial chemistry settings. Kielyov and Armstrong[3] were the first to report a solid-supported version of this reaction, they found that this reaction works well for each reactants immobilized on solid support. Kobayashi and co-workers[4] show that a polymer-supported scandium catalyst catalyze the Greico reaction with high efficiency.
Given the effectiveness of the reaction and the commercial availability of various Greico partners, the Greico three-component coupling is very useful for preparing quinoline libraries for drug discovery.