Olefin Synthesis by Vanadium(V)-Induced Oxidative Decarboxylation-Deoxygenation of 3-Hydroxy Carboxylic Acids

Oxidative decarboxylation of 3-hydroxy carboxylic acids can be effected with various V(V) complexes. This process likely yields an intermediate 1,4-metalla diradical. β-Elimination from this intermediate gives olefin and regenerates V(V), likely as VO₂C1. Thus, although the overall process involves no net change in oxidation state for vanadium, the decarboxylation process is oxidatively induced. Intramolecular trapping of the intermediate yields glycolate and then C-C cleavage products, and skeletal rearrangement gives ketonic products. Qualitatively, rates for oxidative decarboxylation of the acids and the stereospecificity of formation of olefinic products depend on the electron-withdrawing ability of groups attached to vanadium. Methodology is described for the preparation of tri- and tetrasubstituted olefins in high yield from appropriate 3-hydroxy carboxylic acid precursors.