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)2Cl2 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.
Carbonylation of propargyl carbamates with palladium(II) bisoxazoline catalysts: Efficient synthesis of 5-methoxy-3(2H)-furanones
Palladium and CO: Carbonylation of 1 with [Pd(tfa)2(±)- L1] (tfa=trifluoroacetate) affords the spirofuranone 2 with inversion of the stereochemistry at C17 in 96 % yield. C17-epi-1 also gave the same product 2 with retention of the stereochemistry at C17. Labelling studies show that 13CO was incorporated into the C5′ position of the furanone ring. The first asymmetric version of this new reaction was achieved. Copyright