Tungsten carbene alkene

However, the reaction was shown to be catalyzed by a methylidene tungsten-carbene complex rather than the Fischer tungsten carbene complex. They proposed that the reaction would proceed by [2 + 2] cycloaddition of the tungsten carbene complex with the alkyne in Equation (3), ring opening, and another [2 + 2] cycloaddition with the alkene moiety to finally give the cyclized product. 

The reaction of the chromium and tungsten carbene anions [(CO)j-M=C(OMe)CH2 ] (M = W, Cr) with coordinated alkenes has been studied by Beck and co-workers (195,196), as well as by Geoffroy and coworkers (197). The reaction of the carbene anions with cationic complexes having a coordinated ethylene ligand leads to the formation of... 

However, yields in the intermolecular cycloaddition reactions of vinylcarbene complexes, formed by intramolecular insertion of an alkynyl tethered metal carbene complex, are higher when molybdenum rather than chromium or tungsten carbene complexes are employed. Mild thermolysis (THF, 65 °C, 1 h) in the presence of ten equivalents of an electronically undemanding alkene directly leads to the 2-alkyl-2-(2-methoxycyclopentenyl)cyclopropanes 31. ... 

Fischer-type carbenes are known as potential carbene transfer reagents to electron-rich and electron-deficient alkenes. Little is known about the chemistry of carbene complexes with silicon substituents at the carbene C-atom, whereas complexes with germanium, tin, or lead have not yet been prepared. The tungsten-carbene complexes 6 react with an excess of ethyl vinyl ether to give l,2-diethoxy-l-(trialkylsilyl)cyclopropanes 7." Only the f-isomers were formed and similar results can be achieved by using the corresponding molybdenum or chromium complexes. On the other hand, no reaction takes place with 2,3-dihydrofuran or ethyl ( )-but-2-enoate. ... 

The PKR reaction has always been characterized by good functional group compatibility. Examples abound where amines, amides, sulfonamides, sulfides, alcohols, ketones, esters, and silyl ethers are contained in the reactants. In addition, because substituted alkenes react more slowly than unsubstitued alkenes selectivity can be achieved when multiple alkenes are contained in the reactants. An interesting example of functional group compatibility was demonstrated in which a metal carbene not only survived the PKR but accelerated it. For example, the tungsten carbene 19 formed the cyclopentenone 20 in 80% yield at 0 °C. 

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