Ce(OTf)₃‑Catalyzed Multicomponent Reaction of Alkynyl Carboxylic Acids, <i>tert</i>-Butyl Isocyanide, and Azides for the Assembly of Triazole–Oxazole Derivatives

Cerium­(III) triflate-catalyzed multicomponent reactions between alkynyl carboxylic acids, tert-butyl isocyanide, and organic azides have been developed. In the presence of Ce­(OTf)3 (10 mol %), the cascade reaction of one molecule of alkynyl carboxylic acid with three molecules of tert-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 IC50 values below 20 μmol L–1.