Alkene ruthenium-catalyzed

Besides enyne metathesis [66] (see also the chapter Recent Advances in Alkenes Metathesis in this volume), which generally produces 1-vinylcyclo-alkenes, ruthenium-catalyzed enyne cycloisomerization can proceed by two major pathways via hydrometallation or a ruthenacycle intermediate. The RuClH(CO)(PPh3)3 complex catalyzed the cyclization of 1,5- and 1,6-enynes with an electron-withdrawing group on the alkene to give cyclized 1,3-dienes, dialkylidenecyclopentanes (for n=2), or alkylidenecyclopentenes (for n= 1) [69,70] (Eq. 51). Hydroruthenation of the alkyne can give two vinylruthenium complexes which can undergo intramolecular alkene insertion into the Ru-C bond. 

Mascarenas developed a synthetic method to 1,5-oxygen-bridged medium-sized carbocycles through a sequential ruthenium-catalyzed alkyne-alkene coupling and a Lewis-acid-catalyzed Prins-type reaction (Eq. 3.45). The ruthenium-catalyzed reaction can be carried out in aqueous media (DMF/H20 = 10 1).181... 

Directed ruthenium-catalyzed hydroesterifications of alkenes, employing 2-pyridylmethyl formate, leads to esters (Equation (136)). With vinyl ethers a-adducts are obtained (Equation (137)). 

The alkylation of olefinic G-H bonds proceeds when conjugated enones are employed in the ruthenium-catalyzed reaction with alkenes, as shown in Equation (16).1 7 Among the acylcyclohexenes, 1-pivaloyl-l-cyclohexene exhibits a high reactivity and the presence of an oxygen atom at the allylic position in the six-membered ring increases the reactivity of the enones. Some terminal olefins, for example, triethoxyvinylsilane, allyltrimethylsilane, methyl methacrylate, and vinylcyclohexane, are applicable for the alkylation of the olefinic C-H bonds. Acyclic enones also undergo this alkylation. 

Trost and others have extensively studied the ruthenium-catalyzed intermolecular Alder-ene reaction (see Section 10.12.3) however, conditions developed for the intermolecular coupling of alkenes and alkynes failed to lead to intramolecular cycloisomerization due the sensitivity of the [CpRu(cod)Cl] catalyst system to substitution patterns on the alkene.51 Trost and Toste instead found success using cationic [CpRu(MeCN)3]PF6 41. In contrast to the analogous palladium conditions, this catalyst gives exclusively 1,4-diene cycloisomerization products. The absence of 1,3-dienes supports the suggestion that the ruthenium-catalyzed cycloisomerization of enynes proceeds through a ruthenacycle intermediate (Scheme 11). 

Trost et al 2 briefly explored using non-enone enophiles. Simple alkenes led to the formation of complex mixtures of isomers due to the presence of an additional set of /3-hydrogens. Many other types of substrates were incompatible with reaction conditions. Vinyl ketones were, therefore, the only coupling partners shown to be effective in the ruthenium-catalyzed Alder-ene couplings of allenes and alkenes. 

There have also been significant advances in the imido chemistry of ruthenium and osmium. A variety of imido complexes in oxidation states +8 to +6 have been reported. Notably, osmium (VIII) imido complexes are active intermediates in osmium-catalyzed asymmetric aminohydroxyl-ations of alkenes. Ruthenium(VI) imido complexes with porphyrin ligands can effect stoichiometric and catalytic aziridination of alkenes. With chiral porphyrins, asymmetric aziridination of alkenes has also been achieved. Some of these imido species may also serve as models for biological processes. An imido species has been postulated as an intermediate in the nitrite reductase cycle. " ... 

Ruthenium-Catalyzed Cycloaddition Reaction between Enyne and Alkene... 

A solid-phase synthesis of furo[3,2-3]pyran derivatives utilizing highly functionalized sugar templates has been reported <2003JOC9406>. After incorporation of alkenes within the sugar template, such as compound 95, the solid support is introduced via formation of the acid amide. This immobilized system then allows a ruthenium-catalyzed ring-closing metathesis that leads to the formation of the fused oxacycles. 

The catalytic cyclocarbonylations of diynes proceed efficiently to afford fused cyclohexadienes via trapping of the ruthenacyclopentadiene intermediate by an alkene component <2000JA4310>. Thus, the ruthenium-catalyzed cyclo-co-trimerization of 1,6-heptadiyne derivatives possessing a heteroatom at the 4-position affords heterotricycles in good yields (Equation 110). 

SYNPHOS AND DIFLUORPHOS AS LIGANDS FOR RUTHENIUM-CATALYZED HYDROGENATION OF ALKENES AND KETONES... 

Much less information is available about [2 + 2]-cycloadditions. These allow the formation of cyclobutane derivatives in the reaction between two alkenes, or that of cyclobutenes from alkenes and alkynes. The reaction can be achieved thermally via biradical intermediates,543 by photoreaction,544 and there are also examples for transition-metal-catalyzed transformations. An excellent example is a ruthenium-catalyzed reaction between norbomenes and alkynes to form cyclobutenes with exo structure ... 

A ruthenium-catalyzed ring opening cross-metathesis of 8-oxabicyclo[3.2.1]oct-6-en-3-one 1049 with alkenes provides an efficient method for the preparation of substituted tetrahydropyran-4-ones 1050 (Equation 408, Table 50) <1999X8169, 20010L4275>. Similarly, ozone can be used to cleave the same ring system during the synthesis of chiral tetrahydropyran-4-ones <2006T257>. 

Cyclic sulfates provide a useful alternative to epoxides now that it is viable to produce a chiral diol from an alkene. These cyclic compounds are prepared by reaction of the diol with thionyl chloride, followed by ruthenium-catalyzed oxidation of the sulfur (Scheme 9.26).166 This oxidation has the advantage over previous procedures because it only uses a small amount of the transition metal catalyst.167168... 

One of the oldest ruthenium-catalyzed C=C bond coupling reactions deals with the selective dimerization of functionalized alkenes, especially the dimerization of acrylates [ 1,2]. It usually involves either an initial hydrometallation process, oxidative coupling, or vinyl C-H bond activation (Scheme 1). 

One of the most reported pathways for C=C and C=C bonds coupling involves the oxidative coupling and the ruthenacyde intermediate formation. The first ruthenium-catalyzed Unear codimerization of disubstituted alkynes and alkenes involved acrylates or acrylamides and selectively produced 1,3-dienes [33] (Eq. 23). The proposed mechanism involves a ruthenacyclopentene via oxidative coupUng on the Ru(0) catalyst Ru(COD)(COT). The formation of 1,3-di-ene results from intracyclic /1-hydride eUmination, this process taking place only when a favored exocyclic /1-elimination is not possible. 

Recently, cyclopropane derivatives were produced by a ruthenium-catalyzed cyclopropanation of alkenes using propargylic carboxylates as precursors of vinylcarbenoids [51] (Eq. 38). The key intermediate of this reaction is a vinylcarbene complex generated by nucleophilic attack of the carboxylate to an internal carbon of alkyne activated by the ruthenium complex. Then, a [2+1] cycloaddition between alkenes and carbenoid species affords vinylcyclo-propanes. 

Ruthenium vinylidene intermediates have also been proposed in the mechanism of the coupling of unactivated alkenes with terminal alkynes to afford 1,3-dienes as a mixture of two isomers, linear and branched derivatives. The linear one was favored [56] (Eq. 42). The same system has allowed the ruthenium-catalyzed alkenylation of pyridine [57]. 

Selective addition of alkenes and alkynes to aromatic compounds has also been performed by ruthenium-catalyzed aromatic C-H bond activation. Carbon-carbon bond formation occurs at the ortho positions of aromatic compounds, assisted by the neighboring functional group chelation. The reaction, catalyzed by RuH2(CO)(PPh3)3, was efficient with aromatic and heteroaromatic compounds, with various functional groups, and a variety of alkenes and alkynes [ 121 ] (Eq. 90). Activation of vinylic C-H bonds can occur in a similar manner. 

Ruthenium complexes are also suitable catalysts for carbonylation reactions of a variety of substrates. Indeed, when a reaction leads to C-Ru or het-eroatom-Ru bond formation in the presence of carbon monoxide, CO insertion can take place at the coordinatively unsaturated ruthenium center, leading to linear ketones or lactones. Thus, ruthenium-catalyzed carbonylative cyclization was involved in the synthesis of cyclopentenones by reaction of allylic carbonates with alkenes in the presence of carbon monoxide [124] (Eq. 93). 

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