Copper-Catalyzed Reductive Ring-Cleavage of Isoxazoles: Synthesis of Fluoroalkylated Enaminones and Application for the Preparation of Celecoxib, Deracoxib, and Mavacoxib.

We have identified a new reactivity of copper/diamine catalysis for the reductive ring-cleavage of isoxazoles to yield fluoroalkylated enaminones. This protocol has the advantage of using commercially available reagents, ease of setting up, broad tolerance of functionality, and is regiospecific and free of defluorination and reduction of reducible functional groups. The utility was demonstrated by a one-step, regioselective synthesis of fluoroalkylated pyrazole-based drugs such as celecoxib, deracoxib, and mavacoxib.