Ruthenium dioxide ethers

Hydrogenation of this group of pyridines requires little comment. A number of catalysts were employed under a variety of conditions. Ruthenium dioxide is favored in this laboratory in the reduction of these compounds because of the speed of reaction and the absence of side products. 2-(2-Hydroxyethyl)piperidine has been obtained in excellent yield after the hydrogenation of the corresponding pyridine (5). In contrast, a reaction in the presence of Raney nickel at 150° and 130 atm gave less than 50% of reduction product plus di-[2-(2-piperidyl)-ethyl] ether (87). 4-(2-Hydroxyethyl)pyridine has been converted to the piperidine by means of ruthenium catalyst (86a). Brown and Eldred reported that there was no hydrogen uptake using nickel catalysts at 200° and 200 atm (87a). 

Oxidative dimerisation of a guaiacyl system, namely prestegane B, in dichloromethane containing boron trifluoride etherate was achieved in 80% yield by addition to a stirred suspension of ruthenium dioxide dihydrate in dichloromethane containing triflic acid/triflic anhydride (in the proportions 8 2 1) at 0°C followed by reaction for 3 hours (ref.73). 

Method E To a suspension of 0.67 mM of ruthenium(IV) dioxide dihydrate in 0.8 mL of trifluoroacetic acid, 0.4 mL of trifluoroacetic anhydride, and 4 mL of CH2C12 at 0 C is added, with stirring and under argon, a solution of 0.33 mM of prestegane B in 4mL of CH2C12 and, immediately, 0.2 mL of boron trifluoride-diethyl ether complex. After 3 h. the suspended solid is removed by filtration. Evaporation and flash chromatography affords the pure crystalline product yield 84% mp 228-230°C. 

A powerful oxidizer and very reactive material. It has been the cause of many industrial explosions. May explode on heating. Explosive reactions with ammonium chloride, aqua regia + ruthenium, sulfur dioxide solutions in ether or ethanol. Reacts with fluorine to form the explosive gas fluorine perchlorate. 

Pandey S, Baker GA, Kane MA, Bonzagni NJ, Bright FV. O2 quenching of ruthenium(II) tris(2,2 -bypyridyl)2+ within the water pool of perfluoropoly-ether-based reverse micelles formed in supercritical carbon dioxide. Languir 2000 16 5593-5599. 

Huorous compounds are also potentially useful as additives to promote organic reactions in carbon dioxide. For example, a fluorous alcohol RfCH20H assists asymmetric hydrogenations with non-fluorous ruthenium BINAP catalysts, and a fluorous aryl alkyl ether (C8F17C6H4-P-OC12H25) does so in scandium-triflate-catalyzed aldol and Friedel-Crafts reactions. These additives are presumed to act as solubilizers or emulsifiers to promote contact among the various reaction components. Since they are fluorous, they can be readily recovered from the otherwise organic reaction mixtures for reuse. 

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