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Alkenes that are particularly amenable to asymmetric hydrogenation often feature a polar functional group adjacent to the site to be hydrogenated. In the absence of this functional group, catalysis often results in low ee's. For some unfunctionalized olefins, iridium with P,N-based ligands) have proven effective, however. Alkene substrates are ...
The Shi epoxidation is a chemical reaction described as the asymmetric epoxidation of alkenes with oxone (potassium peroxymonosulfate) and a fructose-derived catalyst (1). This reaction is thought to proceed via a dioxirane intermediate, generated from the catalyst ketone by oxone (potassium peroxymonosulfate).
Asymmetric epoxidation is often feasible. [4] One named reaction is the Jacobsen epoxidation, which uses manganese-salen complex as a chiral catalyst and NaOCl as the oxidant. The Sharpless epoxidation using chiral N-heterocyclic ligands and osmium tetroxide. Instead of asymmetric epoxidation, alkenes are susceptible to asymmetric dihydroxylation.
In this aza crown-type, macrocyclic compound, a proton sits between two amide carbonyl oxygens separated by a distance of 2.45 Å. [2]Standard hydrogen bonds are longer (e.g. 2.8 Å for an O···O h-bond), and the hydrogen ion clearly belongs to one of the heteroatoms.
The asymmetric Darzens reaction between aldehydes and (alpha)-haloesters is an effective method for the synthesis of glycidic esters. [25] Chiral auxiliaries, [26] chiral boron enolates, [27] and asymmetric phase transfer catalysis [28] have been used successfully to effect asymmetric induction in the Darzens reaction. (12)
The Juliá–Colonna epoxidation is an asymmetric poly-leucine catalyzed nucleophilic epoxidation of electron deficient olefins in a triphasic system.The reaction was reported by Sebastian Juliá at the Chemical Institute of Sarriá in 1980, [1] with further elaboration by both Juliá and Stefano Colonna (Istituto di Chimica Industriale dell'Università, Milan, Italy).
Enantioselective synthesis, also called asymmetric synthesis, [1] is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric ( enantiomeric or diastereomeric ) products in unequal ...
Wilkinson's catalyst is best known for catalyzing the hydrogenation of olefins with molecular hydrogen. [ 11 ] [ 12 ] The mechanism of this reaction involves the initial dissociation of one or two triphenylphosphine ligands to give 14- or 12-electron complexes, respectively, followed by oxidative addition of H 2 to the metal.