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Metathesis
About: Metathesis is a research topic. Over the lifetime, 9246 publications have been published within this topic receiving 250828 citations.
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TL;DR: The Grubbs' first and second generation catalysts were occluded into crosslinked slabs of polydimethylsiloxane with volumes from 1 mm3 to 1 cm3 by swelling the polymer with catalyst and methylene chloride.
Abstract: The Grubbs' first and second generation catalysts were occluded into cross-linked slabs of polydimethylsiloxane with volumes from 1 mm3 to 1 cm3 by swelling the polymer with catalyst and methylene chloride. Methylene chloride was evaporated under vacuum to yield occluded catalysts where their solvent was polydimethylsiloxane. These occluded catalysts were reacted with alkenes dissolved in H2O or H2O/MeOH mixtures that diffused into the polydimethylsiloxane to react by ring-closing metathesis and cross metathesis. Control experiments revealed that the catalysts remained occluded and metathesis did not occur in the solvent. Occlusion of these catalysts allowed commercially available Grubbs' catalysts to be used with H2O as the solvent while isolating the H2O sensitive ruthenium methylidene from exposure to H2O. Functional group selective experiments were carried out where the polydimethylsiloxane was an “active” membrane to exclude salts. Polydimethylsiloxane is a hydrophobic polymer, so the deprotonated sa...
TL;DR: In this paper, the stereochemical outcome of allylation reactions with these aldehydes was found to be dependent upon both the choice of protecting groups for the 2'- and 3'-hydroxyl groups and, to some extent, the nature of the Lewis acid catalyst employed.
Abstract: alpha-Phosphono lactone derivatives of the nucleosides cytidine and cytosine arabinoside have been prepared from the corresponding nucleoside aldehydes. The stereochemical outcome of allylation reactions with these aldehydes was found to be dependent upon both the choice of protecting groups for the 2'- and 3'-hydroxyl groups and, to some extent, the nature of the Lewis acid catalyst employed. Ultimately, conditions were found that favored either the 5'R or 5'S diastereomer from different cytidine aldehydes, and gave some stereoselectivity in additions to an aldehyde derivative of ara-C. The resulting homoallylic alcohols were used as substrates in attempted Knovenagel and Horner-Wadsworth-Emmons condensations, but elimination was found to predominate over lactone formation under the conditions employed. The desired alpha-phosphono lactones could be prepared through a reaction sequence that included ring-closing metathesis on acrylate esters of the homoallylic alcohols, followed by reduction of the resulting alpha,beta-unsaturated lactones and carbon-phosphorus bond formation on enolates generated from the saturated lactones.
TL;DR: In this article, the metathesis of allyl cyanide was carried out by the action of a catalytic system containing tungsten hexachloride by 1,1,3,3-tetramethyl-1, 3-disilacyclobutane.
Abstract: The metathesis of allyl cyanide was carried out by the action of a catalytic system containing tungsten hexachloride by 1,1,3,3-tetramethyl-1,3-disilacyclobutane.
TL;DR: In this paper, the contributions mainly from authors' laboratory on applications of the various metathetic processes for synthesis of natural products and related molecules are discussed, including ring closing, ring opening, cross-metathesis, enyne metathesis and domino processes.
Abstract: Exchange of an alkene unit of an olefinic compound with alkene unit of another compound (metathesis) leads to a new olefinic compound. This process takes place in presence of a transition metal alkylidine complex as catalyst. A variety of synthetic operations such as ring closing metathesis, ring opening metathesis, cross metathesis, enyne metathesis and domino processes involving ring opening-ring closing and cross metathesis can be achieved to construct novel molecular architectures that are difficult to make by other reactions. This account presents briefly the contributions mainly from authors’ laboratory on applications of the various metathetic processes for synthesis of natural products and related molecules.