VO (OR) Cl
2 is revealed to be a Lewis acid with one-electron oxidation capability. The regioselective ringopening oxygenation of cyclic ketones is catalyzed by VO (OEt) Cl
2 in ethanol under oxygen to give the diesters or keto esters. The presence of α, β carbon-carbon double bond in the ketones alters the reaction course. 2-Cyclohexen-l-ones undergo dehydrogenative aromatization to give aryl ethers. An oxovanadium compound obtained from VO (OEt) Cl
2 and AgOTf or Me
3SiOTf works more efficiently. In the cases of 2-cyclopenten-1- ones, 1-acetyl-1-cyclohexene, and β-ionone, allylic oxidation is achieved to introduce an oxo or alkoxyl group at the γ-position. 2-Phenylglycine derivatives are transformed to ethyl benzoate and ethyl phenylglyoxylate by the VO (OEt) Cl
2-induced' oxidative deamination and/or decarboxylation. The ring-opening addition of cyclobutanone to olefins bearing an electron-withdrawing group leads to the corresponding E-chloro ester via oxidation of a cyclobutoxide intermediate. Treatment of a mixture of diketene and styrenes with VO (OR) Cl
2 gives 3-alkoxycarbony1-2-methyl-5-phenyl-4, 5-dihydrofurans.
Oxidative desilylation is selectively realized by one-electron oxidation of organosilicon compounds with VO (OEt) Cl
2. Silyl enol ethers undergo the oxidative cross coupling to afford unsymmetrical 1, 4-diketones. Allylic silanes also regioselectively dimerize to 1, 5-hexadienes. Oxidative desilylation of silyl enol ethers and allylic silanes selectively gives γ, δ-unsaturated ketones depending on their redox potentials.
The highly stereoselective monodebromination of
gem-dibromocyclopropanes is induced or catalyzed by a low valent vanadium species generated from vanadium (III) chloride or CpV (CO)
4 and zinc in dimethoxyethane in a combination with diethyl phosphonate or triethyl phosphite.
View full abstract