Second-Generation Process for the HCV Protease Inhibitor BILN 2061: A Greener Approach to Ru-Catalyzed Ring-Closing Metathesis†

The ring-closing metathesis (RCM) step, a key reaction in our process to BILN 2061, was dramatically improved from the first-generation process by the selection of a more appropriate substrate as well as the use of a more effective catalyst. The two RCM reactions are compared in detail using criteria that are of high significance to the process chemist.