Ruthenium-Catalyzed Oxidation for Organic Synthesis

2-Dihaloalkenes are oxidized to a-diketones in a variety of norbornyl derivatives, which can serve as highly potent and inextricable templates for strained polycyclic unnatural compounds (Eq. (7.9)) [22]. 

Aromatic and furan rings are smoothly converted into carboxylic acids (Eqs. (7.10) and (7.11)) [23], Terminal alkynes undergo a similar oxidative cleavage to afford carboxylic acids, while internal alkynes are converted into diketones (Eq. (7.12)) [24, 25], 

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The oxidation of N-methylamines provides various useful methods for organic synthesis. Selective demethylation of tertiary methylamines can be carried out by the ruthenium-catalyzed oxidation and subsequent hydrolysis (Eq. 3.71). This is the first synthetically practical method for the N-demethylation of tertiary amines. The methyl group is removed chemoselectively in the presence of various alkyl groups. 

An important factor in the success of these reactions involves chelation-assistance by a heteroatom. Thus, the coordination of the heteroatom to the metal, brings the metal closer to the C-H bond and stabilizes the thermally unstable C-M-H species formed by the oxidative addition of a C-H bond to a low-valent transition metal complex. In addition, the use of the chelation-assistance leads to a high regioselectivity, which is an essential factor in organic synthesis. For reactions, a number of transition metal complexes - including ruthenium, rhodium, and iridium - are used as a catalyst, and ruthenium-catalyzed reactions will be described in this chapter [5]. 

Ruthenium compounds are widely used as catalysts in organic synthesis and have been extensively studied as catalysts for the aerobic oxidation of alcohols In 1978, Mares and coworkers reported that RuCls.nHjO catalyzes the aerobic oxidation of secondary alcohols into the corresponding ketones, albeit in modest yields. Subsequently, RUCI3 and RuCl2(Ph3P)j were shown to catalyze the aerobic oxidation of activated allylic and benzylic alcohols under mild conditions, e.g. the oxidation of retinol to retinal (Reaction 2). 

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