Rh-Catalyzed Conjugate Addition of Aryl and Alkenyl Boronic Acids to α-Methylene-ß-lactones: Stereoselective Synthesis of trans-3,4-Disubstituted ß-Lactones.

A one-step preparation of 3,4-disubstituted ß-lactones through Rh-catalyzed conjugate addition of aryl or alkenyl boronic acids to α-methylene-ß-lactones is described. The operationally simple, stereoselective transformation provides a broad range of ß-lactones from individual α-methylene-ß-lactone templates. This methodology allowed for a direct, final-step C-3 diversification of nocardiolactone, an antimicrobial natural product.