Tethered metathesis reaction

Rodriguez-Escrih, C., Urpi, F., and Vilarrasa, J. (2008) StereocontroDed total synthesis of amphidinohde X via a sihcon-tethered metathesis reaction. Org. Lett., 10, 5191-5194. 

Similar systems were independently developed by other research groups [139,140] using arene functionalised NHC ligands in an attempt to improve the catalytic system. Semeril et al. developed a tethered system from an earlier untethered one [197] that was used in olefin metathesis reactions after initial loss of the arene (p-cymene) ligand (see Figure 4.67). 

Cyclopentadienyl compounds of the form CpCo(CO)2 are also known to convert l,n-enynes into the tranditional 1,3-diene cycloisomerization products (486, 487). Remarkably, the metathesis reaction is independent of tether length between both unsaturated functional groups, and leads to five-membered ring carbocycles exclusively (Scheme 60). 

Olefin metathesis reaction that reorganizes carbon-carbon double bonds provides fundamentally new strategies for natural product synthesis and polymer chemistry. Hilvert and coworkers built up an artificial metalloenzyme by covalently tethering a Grubbs-Hoveyda-type Ru complex to a protein scaffold [78]. An /V-heterocyclic carbene (NHC) ligand, which has been reported as a suitable ligand for a number of water-soluble ruthenium-based metathesis catalysts, was derivatized with an electrophilic bromoacetamide. The Ru carbene complex (27 in Figure 10.16) was then attached by site-selective alkylation of the cysteine... 

Silicon has also been employed as a tether for directing ringclosing metathesis (RCM) reactions. The RCM precursors 38 were generated by attachment of chlorodimethylvinylsilane to alkenyl alcohols. An olefin metathesis reaction using Schrock s catalyst provided the cyclized products 39 in excellent yields (eq 18). Although Grubbs catalyst had been successfully employed in the case of allylsiloxy dienes, Schrock s catalyst resulted in better yields in the case of the vinylsiloxy dienes 39. Oxidative cleavage of the silicon tether was then used to provide acyclic hydroxyaldehydes. 

SCHEME 38 Ring-closing metathesis reaction of ester-tethered dienes. 

Evans PA, Cui J, Buffone GP. Diastereoselective temporary silicon-tethered ring-closing-metathesis reactions with prochiral alcohols a new approach to long-range asymmetric induction. Angew. Ghem. Int. Ed. 2003 42 1734-1737. 

Temporary Silicon-Tethered Ring-Closing Metathesis Reactions in Natural Product Synthesis... 

Temporary Silicon—Tethered Ring—Closing Metathesis Reactions I 233... 

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