Ruthenium RuCl3-catalyzed oxidation

The oxidation reaction of /3-lactams can be extended to the aerobic oxidation reaction [141], Typically, the RuCl3-catalyzed oxidation of /3-lactam 70 with molecular oxygen (1 atm) in the presence of acetaldehyde and sodium carboxylate gave the corresponding 4-acyloxy /3-lactam 71 in 91% yields (d.e. >99%) (Eq. 3.83). This aerobic oxidation gives peracetic acid in situ by ruthenium-catalyzed reaction of acetaldehyde with molecular oxygen, and hence similar results with those obtained by the oxidation with peracetic acid. 

Besides ruthenium tetroxide, other ruthenium salts, such as ruthenium trichloride hydrate, may be used for oxidation of carbon-carbon double bonds. Addition of acetonitrile as a cosolvent to the carbon tetrachloride-water biphase system markedly improves the effectiveness and reliability of ruthenium-catalyzed oxidations. For example, RuCl3 H20 in conjunction with NaI04 in acetonitrile-CCl4-H20 oxidizes (Ej-S-decene to pentanoic acid in 88% yield. Ruthenium salts may also be employed for oxidations of primary alcohols to carboxylic acids, secondary alcohols to ketones, and 1,2-diols to carboxylic acids under mild conditions at room temperature, as exemplified below. However, in the absence of such readily oxidized functional groups, even aromatic rings are oxidized. 

Fig. 21. Ruthenium-catalyzed Oxidative cleavage of 9,10-dihy-droxystearic acid methyl ester by H2O2 in a two-phase system. Conditions RuCl3 DDAB diol H302 = 1 20 500 4000 (molar) 2 h at 80°C in 1,2-dicholethane. DDAB, didodecyidimethyl ammonium bromide.

The ruthenium-catalyzed oxidation of nitriles takes place at the a-position to nitriles. For example, the RuCl3-nH20-catalyzed oxidation of benzylcyanide with f-BuOOH gives benzoylcyanide in 94% yield [137]. 

A high-valent ruthenium complex is also reported to cleave the sp C-H bond. RuCl3 -3H20 catalyzes the transformation of cyclic alkanes to the corresponding ketones in the presence of peracetic acid, where oxoruthenium species is considered to act as the active species. Alcohol, as a primary product in this oxidation reaction, is obtained as an intermediate in the presence of trifluoroacetic acid (Scheme 14.11) [25]. 

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