Olefins electron-rich, carbene complex synthesis

Electron-rich olefins such as 36 have been used by Lappert in the synthesis of a great number of mono-, bis-, tris-, and tetrakiscarbene complexes from various transition metal species (62). Ru, Os, and Ir carbene complexes have been prepared from reactions with these olefins, e.g.,... 

In addition to reactions characteristic of carbonyl compounds, Fischer-type carbene complexes undergo a series of transformations which are unique to this class of compounds. These include olefin metathesis [206,265-267] (for the use as metathesis catalysts, see Section 3.2.5.3), alkyne insertion, benzannulation and other types of cyclization reaction. Generally, in most of these reactions electron-rich substrates (e.g. ynamines, enol ethers) react more readily than electron-poor compounds. Because many preparations with this type of complex take place under mild conditions, Fischer-type carbene complexes are being increasingly used for the synthesis [268-272] and modification [103,140,148,273] of sensitive natural products. 

Finally, an additional synthesis of recent times (1971) comes from Lappert and his group (48). They treated an electron-rich olefinic system, such as 1, l, 3,3 -tetraphenyl-2,2 -biimidazolidinylidene, with a suitable complex compound. In this manner, they attained cleavage of the C=C double bond and attachment of the carbene fragment to the metal ... 

Hitchcock, P.B., Lappert, M.F., Pye, P.L., Thomas, S., Carbene complexes. Part 16. Synthesis and properties of NN N"N" -tetra-aiyl-substituted electron-rich olefin-derived carbeneruthenium(II) complexes containing a spontaneously formed ort/io-metallated-N-arylcarbene ligand, J. Chem. Soc., Dalton Trans. 1979, 1929-1942. 

Reviews.—Recent reviews involving olefin chemistry include olefin reactions catalysed by transition-metal compounds, transition-metal complexes of olefins and acetylenes, transition-metal-catalysed homogeneous olefin disproportionation, rhodium(i)-catalysed isomerization of linear butenes, catalytic olefin disproportionation, the syn and anti steric course in bi-molecular olefin-forming eliminations, isotope-elfect studies of elimination reactions, chloro-olefinannelation, Friedel-Crafts acylation of alkenes, diene synthesis by boronate fragmentation, reaction of electron-rich olefins with proton-active compounds, stereoselectivity of carbene intermediates in cycloaddition to olefins, hydrocarbon separations using silver(i) systems, oxidation of olefins with mercuric salts, olefin oxidation and related reactions with Group VIII noble-metal compounds, epoxidation of olefins... 

First synthetic attempts with compound 11 using catalyst [Ru]-VII [17] delivered the undesired bicyclic structure 12, which results from the initial attack of the ruthenium carbene complex at the terminal olefin via intermediate 13 (Scheme 11.5). To direct the initiation of the catalytic cycle into the other double bond, through intermediate 14, Honda et al. decided to introduce steric hindrance using a disub-stituted olefin in the alkyl chain. Their results showed, however, that the resulting compound was not reactive enough to undergo metathesis under the chosen reaction conditions. With the use of a more electron-rich allyl ether moiety such as in 15, it was possible to isolate the desired product in 74% yield and successfully complete the synthesis of securinine. Ruthenium complexes [Ru]-I and [Ru]-II were... 

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