Ruthenium olefin cleavage

Figure 3.31 Catalytic cycle of the ruthenium-catalysed cleavage of olefins in the presence of percarboxylic acids.

Use of the chiral carbon pool for cyclopentenone preparation is also known. The fungal metabolite terrein [88] was selectively monoacetylated and then reduced with chromous chloride to enone [89]. Acetylation and olefin cleavage with ruthenium tetroxide aiwi sodium periodate led to aldehyde [90], which was readily decarbonylated to [65] (51). An alternative route (52) began with the less common S,S-tartaric acid [91], converted in four steps to diiodide [92]. Dialkylation of methyl methylthiomethyl sulfoxide with [92] gave the cyclopentane derivative [93]. Treatment of [93]... 

High-valent ruthenium oxides (e. g., Ru04) are powerful oxidants and react readily with olefins, mostly resulting in cleavage of the double bond [132]. If reactions are performed with very short reaction times (0.5 min.) at 0 °C it is possible to control the reactivity better and thereby to obtain ds-diols. On the other hand, the use of less reactive, low-valent ruthenium complexes in combination with various terminal oxidants for the preparation of epoxides from simple olefins has been described [133]. In the more successful earlier cases, ruthenium porphyrins were used as catalysts, especially in combination with N-oxides as terminal oxidants [134, 135, 136]. Two examples are shown in Scheme 6.20, terminal olefins being oxidized in the presence of catalytic amounts of Ru-porphyrins 25 and 26 with the sterically hindered 2,6-dichloropyridine N-oxide (2,6-DCPNO) as oxidant. The use... 

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

Treatment of tetrahydroberberine (26) with sodium benzenethiolate (48) or -selenolate (49) in the presence of ruthenium catalyst afforded the C-14—N bond cleavage products 51 or 52 with a phenylthio or phenylseleno group at C-14 (Scheme 12). The latter was converted to the 10-membered amino olefin 53 on treatment with m-chloroperbenzoic acid. 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

A proposed mechanism for the isomerization is illustrated in Fig. 1. The ruthenium complex first coordinates to the olefin and transfers it from a terminal position to an internal position, providing an allyl alcohol [17,18]. The allyl alcohol is then converted to either another allyl alcohol through C-O cleavage (route a) or a ketone through C-H cleavage (route b). 

The oxidation catalyst is believed to be ruthenium tetraoxide based on work by Engle,149 who showed that alkenes could be cleaved with stoichiometric amounts of ruthenium tetraoxide. Suitable solvents for the Ru/peracid systems are water and hexane, the alkene (if liquid) and aromatic compounds. Complex-ing solvents like dimethylformamide, acetonitrile and ethers, and the addition of nitrogen-complexing agents decrease the catalytic system s activity. It has also been found that the system has to be carefully buffered otherwise the yield of the resulting carboxylic acid drops drastically.150 The influence of various ruthenium compounds has also been studied, and generally most simple and complex ruthenium salts are active. The two exceptions are Ru-red and Ru-metal, which are both inferior to the others. Ruthenium to olefin molar ratios as low as 1/20000 will afford excellent cleavage yields (> 70%). vic-Diols are also... 

Figure 3.33 Catalytic cleavage of olefins using a mixed ruthenium (If )/molybdenum (VI)/hydrogen peroxide system.

Fig. 4.34 A catalytic cycle for ruthenium-catalyzed oxidative cleavage of olefins.

Copper compounds are catalysts for the Michael addition reaction (249), olefin dimerizations (245, 248), the polymerization of propylene sulfide (142), and the preparation of straight-chain poly phenol ethers by oxidation of 2,6-dimethylphenol in the presence of ethyl- or phenyl-copper (209a). Pentafluorophenylcopper tetramer is an intriguing catalyst for the rearrangement of highly strained polycyclic molecules (116). The copper compound promotes the cleavage of different bonds in 1,2,2-tri-methylbicyclo[1.1.0]butane compared to ruthenium or rhodium complexes. Methylcopper also catalyzes the decomposition of tetramethyllead in alcohol solution (78, 81). 

Another example for methoxy functionalised imidazolium salts comes from the group of Cetinkaya [185,186] featuring an -alkyl tether. Cetinkaya etal.me the traditional route to transition metal carbene complexes employing the electron-rich olefins as carbene source [57-59], Thermal cleavage of the olefinic double bond in the presaice of the metal precursor complex yields the desired transition metal carbene complex (see Figure 3.66). Using this method, Cetinkaya et al. synthesised rhodium(l) [185,186] and ruthenium(ll) [185] complexes. 

The mono-pincer ruthenium(II) complex was successfuUy employed in the oxidative cleavage of olefins to aldehydes, dialdehydes or keto-aldehydes. 

Preparation of (R)-l involves the chlorination of (R)-l,l-bina-phthyl-2,2-dicarboxylic acid with scc-BuLi and hexachloro-ethane. Condensation of the resulting dichorinated product with 3-chloro-2-chloromethyl-l-propene, followed by oxidative cleavage of the olefin moiety with ruthenium trichlorde affords (R)-l in modest yields. 

This reaction is considered to proceed via initial coordination of pyridine to one of ruthenium centers, after which the adjacent ruthenium cleaves the ortho C-H bond followed by successive insertion of CO and olefin. When 2-phenylpyridine is employed in a similar system, acylation in the phenyl ring takes place via prior coordination of the N atom followed by cleavage of proximal C-H bond in the phenyl group (Scheme 14.7) [19]. 

Various vinylsilanes, olefins or acetylenes insert into the ortho C-H bond of aromatic ketones in the presence of catalytic amount of ruthenium complexes in high yields [21,22], The C-H bond cleavage reaction of aromatic ketones also involves orthometallation which is promoted by prerequisite coordination of the carbonyl group to ruthenium (Scheme 14.9) [21], This type of reaction has a wide generality for aromatic and alkenyl ketones with a variety of alkenes. 

Overhand, Overkleeft and their collaborators have synthesised a variety of SAAs [39]. The synthesis of Fmoc-protected 6 ( Fig. 2) is illustrated in Scheme 2 [15]. Tri-O-acetyl-D-glu-cal was converted into the SAA precursor 43 in five steps. Formation of the trichloroacetimi-date derivative 44 and a subsequent Overman rearrangement was used to introduce the amino group onto the pyran scaffold giving 45. Hydrogenation of the olefin in 45 was accompanied by cleavage of the silyl ether to afford the primary alcohol which was oxidised with a catalytic amount of ruthenium (III) chloride in the presence of sodium periodate giving 46. Subjection... 

As an oxometal component, osmium tetroxide is the most reliable reagent on the laboratory scale to produce c/s-diols. Ruthenium tetroxide in the presence of NaI04 effects oxidative cleavage of olefins [4], but has been successfully employed for so-called lightning dihydroxylation reactions using a two-phase medium [6]. 

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