Several organic transformations were found to be catalyzed by methylrhenium trioxide, CH[subscript]3ReO[subscript]3 (MTO): decomposition of ethyl diazoacetate (EDA) to 2-butenedioic acid diethyl esters; cycloadditions of EDA with imines (to aziridines), with olefins (to cyclopropanes), and with aldehydes or ketones (to epoxides). In the presence of MTO, the reactions of EDA with alcohols, phenols, thiols or amines yield, respectively, the corresponding [alpha]-alkoxy, [alpha]-phenoxy, [alpha]-thio ethyl acetate or ethyl glycine esters. These reactions occur under mild conditions and give satisfactory to high product yields;The other reactions catalyzed by MTO are dehydration of alcohols to ethers and olefins; direct amination of aromatic alcohols, and the disproportionation of alcohols to alkanes and carbonyl compounds;MTO activates H[subscript]2O[subscript]2 through the formation of two active species (mono-peroxo-Re(VII) A, and bisperoxo-Re(VII), B). These two peroxo species oxidize alkynes to the corresponding 1,2-dicarbonyl compounds or carboxylic acids, and anilines to nitroso benzenes or N-oxides in high yields. Tertiary phosphines are oxidized by molecular oxygen to the corresponding phosphine oxides in the presence of MTO. Similarly oxygen transfer from sulfoxides, epoxides, N-oxides, triphenylarsine oxide and triphenylstibine oxide to triphenylphosphine is also catalyzed by MTO. The reactions of MTO and epoxides yield bis(alkoxy)rhenium(VII) complexes.