Selective Synthetic Transformations Based on Vanadium-Mediated Redox Reactions

Abstract

Low-valent vanadium-, or titanium-catalyzed reduction reactions including dehalogenation, pinacol coupling, and the related radical reaction have been developed by constructing a multi-component redox system in combination with a co-reductant and an additive, which serve for the recycling and liberation of the catalyst. High stereoselectivity is attained in these catalytic transformations. Oxovanadium (V) compounds, which are evaluated as Lewis acids with oxidation capability, induce one-electron oxidative desilylation of organosilicon compounds such as silyl enol ethers, allylic silanes, and benzylic silanes, allowing chemoselective-catalyzed with the less oxidizable organosilicon compounds. The oxovanadium (V) -induced or catalyzed oxidation of benzylsilane and benzyltin compounds is carried out under oxygen atmosphere to afford aromatic aldehydes (ketones) and/or carboxylic acids. Oxidative ligand coupling of dialkylarylaluminums is achieved by treatment with oxovanadium (V) compounds, leading to the formation of the alkylarenes. The ate complexes derived from arylaluminums or 1-alkenylaluminums and 1-alkynyllithiums undergo facile oxidative ligand coupling. Similar oxidation is observed with organoborons and organozincs or their ate complexes. This method is applied to vicinal dialkylation with the diorganozincs or ate complexes at both the α and β positions of 2-cycloalkenones.