Substituent effects were studied in a series of aromatic cyclic seleninate esters and spirodioxyselenuranes that function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. The methoxy-substituted selenurane proved the most efficacious catalyst for the reduction of hydrogen peroxide with benzyl thiol, and the reaction rates were enhanced for both classes by electron-donating substituents. Hammett plots indicated rho = -0.45 and -3.1 for the seleninates and selenuranes, respectively, suggesting that oxidation at Se is the rate-determining step in their catalytic cycles.

Cyclic seleninate esters serve as catalysts for the rapid oxidation of sulfides to sulfoxides, alkenes to epoxides, and enamines to α-hydroxyketones. Optimal conditions were found that minimize the overoxidation of the product sulfoxides to sulfones and the hydrolysis of epoxides to diols. In some examples such as styrene derivatives, oxidative cleavage was observed instead of epoxidation. The enamine oxidations proceed via the initial formation of dimeric 2,5-diamino-1,4-dioxane species, which were hydrolyzed in situ to the final products. The structure of one such dimer was confirmed by X-ray crystallography.

Cyclic Seleninate Esters as Catalysts for the Oxidation of Sulfides to Sulfoxides, Epoxidation of Alkenes, and Conversion of Enamines to α-Hydroxyketones. -Generally, the seleninate efficiently promotes the reactions. However, some limitations are observed. For example, the enamines (XIc) and (XId) as well as sterically hindered enamines do not yield the corresponding α-hydroxyketones and starting from electron-deficient alkenes and styrenes no epoxides are obtained. The formation of α-hydroxyketones proceeds via dimeric intermediates as is confirmed by isolation of the derivative (XIV). -(MERCIER, E. A.; SMITH, C. D.; PARVEZ, M.; BACK*, T. G.; J. Org. Chem. 77 (2012) 7, 3508-3517, http://dx.