Kinetics and Mechanism of the Dihydroxylation and Epoxidation of Conjugated Dienes with Hydrogen Peroxide Catalyzed by Methylrhenium Trioxide.
The title reactions occur readily. With acetonitrile chosen as the solvent, 17 of them were studied by kinetic methods. As is true for other MTO-catalyzed reactions, peroxorhenium complexes are the active species. Under the conditions of hydrogen peroxide present in large excess, usually employed here, CH(3)Re(O)(eta(2)-O(2))(2)(OH(2)) was the major reactive catalyst present. The rate constant between it and the dienes increase or decrease as substituents add or remove electron density from the C=C bonds, suggesting a concerted mechanism in which the double bond attacks a peroxide oxygen. Many of the products are diols, some rearranged, except when the stability of carbocation intermediates for epoxide ring opening are so unstable as to prolong their lives. When urea-hydrogen peroxide was used instead, the monoepoxides were obtained.
Tan
Haisong
H
Ames Laboratory and Department of Chemistry, Iowa State University, Ames, Iowa 50011.
Espenson
James H.
JH