Ligand-controlled Palladium-catalyzed Carbonylation of Alkynols: Highly Selective Synthesis of α-Methylene-β-lactones.

The first general and regioselective Pd-catalyzed cyclocarbonylation to give α -methylene- β -lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N -arylated imidazole ( L11 ) in the presence of Pd(MeCN) 2 Cl 2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α -methylene- β -lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products.