A Novel Method for the Preparation of Acid-Sensitive Epoxides from Olefins with the Combined Use of Molecular Oxygen and Aldoacetal Catalyzed by a Cobalt(II) Complex
An efficient synthesis of acid-sensitive epoxides, such as chromene oxide or epoxide of γ,δ-unsaturated alcohol, was successfully achieved by the oxygenation of corresponding olefins with the combined use of an atmospheric pressure of molecular oxygen and aldoacetal catalyzed by a cobalt(II) complex coordinated with the 1,3-diketone ligand. The reactions proceeded under mild and neutral conditions
In the presence of a catalytic amount of cobalt(II)-Schiff base complexes, various olefins are smoothly oxygenated into the corresponding epoxides in good to high yields by combined use of an atmospheric pressure of oxygen (oxidant) and cyclic ketones (reductant), such as 2-methylcyclohexanone, under mild conditions.
In the presence of bis(3-methyl-2,4-pentanedionato)cobalt(II) complex catalyst, various trisubstituted olefins are smoothly monooxygenated into the corresponding epoxides in high yields under neutral conditions by the combined use of molecular oxygen and propionaldehyde diethyl acetal.
Epoxidation of olefins by β-bromoalkoxydimethylsulfonium ylides
作者:George Majetich、Joel Shimkus、Yang Li
DOI:10.1016/j.tetlet.2010.10.068
日期:2010.12
Olefins can be converted to their respective epoxides in a one-pot procedure by dissolving the olefin in anhydrous DMSO, adding NBS to the reaction mixture to generate a beta-bromoalkoxydimethylsulfonium ylide, and then adding DBU to the reaction mixture. A large variety of alkenes were successfully epoxidized with yields largely dependent on the structure of the alkene. Most importantly, the facial selectivity of this one-pot process is the opposite of that observed when using traditional epoxidizing reagents. Electron-poor alkenes are not epoxidized under these conditions. (C) 2010 Published by Elsevier Ltd.