Ruthenium reagents

Ruthenium Reagents. Ruthenium compounds are powerful oxidizing agents that are capable of cleaving alkenes. In Table 3.1, ruthenium tetroxide (RuOq) showed a reduction potential of 0.59 V in the following reaction  

A key ingredient in the RuCl3/NaI04 oxidation appears to be the choice of solvent, with acetonitrile being preferred. Under these reaction conditions, alkenes such as 1-nonene are cleaved to acids (nonanoic acid, 89% yield). Alcohols (see 332) can be oxidized to the acid (in this case forming 333 without disturbing the 

In some cases, secondary reactions can accompany the oxidation. In Silverstein s synthesis of optically pure grandisol,4 l 334 was opened to the diacid (335), which gave ketone 336 after oxidative decarboxylation under the reaction conditions. 

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H3Ru4(CO)n] ,136,137 and [Ni6(CO)12]2".329331 332 344 345 347-348 The products from these reactions are quite varied, so it is hard to generalize. Most of those obtained from the iron and ruthenium reagents are conventional small clusters of the type EM3, EM4, or E2M4. The reactions with... 

The results of a recent study published by Katsuki and co-worlcers include improvements in the enantiomeric excess of binaphthol formation using chiral (NO)Ru(II)-(salicylidene) ethylenediamino (salen) complex 214 (Figure 7) [142]. The reaction was conducted under aerobic conditions so that dioxygen generated the active ruthenium reagent (Scheme 55). Yields of binaphthol as high as 95 % were realized. 

Oxidative Cleavage Reactions. Among the numerous methods for 1,2-diol cleavage there exist only a few that involve catalytic ruthenium reagents, for example Ruthenium(III) Chloride with Sodium Periodate Attempted selective monooxidation of a 1,2-diol to the hydroxy aldehyde with catalytic TPAP and NMO resulted in carbon-carbon bond cleavage to provide the aldehyde (eq 11). Furthermore, attempted oxidation of an anomeric a-hydroxy ester failed instead, in this case decarboxy-lation/decarbonylation and formation of the lactone was observed (eq 12). However, Dimethyl Sulfoxide-Acetic Anhydride provided the required a-dicarbonyl unit. Retro-aldol fragmentations can also be a problem. ... 

First, on completion of the reaction, the ruthenium reagent is easily removed by filtration through a thin pad of silica gel and, second, in the presence of a co-oxidant, such as A-methylmorpholine A-oxide, only a catalytic amount of ruthenium reagent ((n-Pr)4N+Ru04, TPAP) is needed. The role of the co-oxidant is to regenerate the Ru(VII) after its reduction as a consequence of alcohol oxidation. While the details of the exact pathway are unknown. Scheme 8.8 provides a potential pathway to account for the oxidation shown in item 11 in Table 8.5. 

Sharpless oxidation method (RuCls, NaI04 in CHsCN-CC -water) has been shown to oxidise 2, 3 -0-isopropylidene derivatives of ribonucleosides to the uronic acid nucleosides in very high yield under mild, neutral conditions, and potassium persulfate is also effective for recycling the ruthenium reagent in such oxidations the latter procedure was used to make, inter alia, the uronic acid analogue of ACT. Oxidation of isopropylidene uridine with CrOa, PCC or PDC in the presence of acetic anhydride leads to the formation of lactone nucleoside 154 in 50% yield, and several similar cases were reported,... 

Thus, Mathis et al. [1, 2] investigated oxidation reactions with 4-nitroperbenzoic acid, sodium hypobromite, osmium tetroxide and ruthenium tetroxide. Hamann et al. [3] employed phosphorus oxychloride in pyridine for dehydration. However, this method is accompanied by the disadvantages that the volume applied is increased because reagent has been added and that water is sometimes produced in the reaction and has to be removed before the chromatographic separation. 

Moriarty, R.M. Penmasta, R. Awasthi, A.K. Prakash, I. / Org. Chem., 1988, 53, 6124. Ruthenium tetroxide is an expensive reagent, but the cost can be greatly reduced by the use of an inexpensive cooxidant such as NaOCl, the function of which is to oxidize RUO2 back to ruthenium tetroxide. 

Scheme 31 Synthesis of ruthenium and rhenium disulfido complexes by the use of (TMS)2S as a sulfur reagent...

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