Ce(OTf)-Catalyzed Multicomponent Reaction of Alkynyl Carboxylic Acids, -Butyl Isocyanide, and Azides for the Assembly of Triazole-Oxazole Derivatives.

Cerium(III) triflate-catalyzed multicomponent reactions between alkynyl carboxylic acids, -butyl isocyanide, and organic azides have been developed. In the presence of Ce(OTf) (10 mol %), the cascade reaction of one molecule of alkynyl carboxylic acid with three molecules of -butyl isocyanides proceeds chemoselectively and regioselectively via a triple and ordered isocyanide insertion process at room temperature, and then the cesium-catalyzed [3 + 2] cycloaddtion reaction between the resulted alkynyl oxazole and organic azides was further initiated by the temperature elevation (100 °C), thereby leading to multisubstituted triazole-oxazole derivatives in practical, time-saving, one-pot operations. Furthermore, some of the synthesized target compounds showed potential anticancer activities against MGC803 (human gastric cancer cell) with IC values below 20 μmol L.