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The rule states that with the addition of a protic acid HX or other polar reagent to an asymmetric alkene, the acid hydrogen (H) or electropositive part gets attached to the carbon with more hydrogen substituents, and the halide (X) group or electronegative part gets attached to the carbon with more alkyl substituents. This is in contrast to ...
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 ...
About a decade later, Jurkauskas and Buchwald also utilized dynamic kinetic resolution towards the hydrogenation of conjugated systems. [8] 1,4 addition to cyclic enones is quite common in many reaction schemes, however asymmetric reductions in the presence of an easily epimerizable center adds to the complexity when trying to modify only one center.
For small rings (fewer than eight atoms), a trans alkene cannot be achieved without substantial ring and angle strain (the p orbitals are improperly aligned for a π bond). Bredt's rule also applies to carbocations and, to a lesser degree, free radicals, because these intermediates also prefer a planar geometry with 120° angles and sp 2 ...
K. Barry Sharpless was the first to develop a general, reliable enantioselective alkene dihydroxylation, referred to as the Sharpless asymmetric dihydroxylation (SAD). Low levels of OsO 4 are combined with a stoichiometric ferricyanide oxidant in the presence of chiral nitrogenous ligands to create an asymmetric environment around the oxidant.
Non-carbon nucleophiles such as water, alcohols, amines, and enamines can also react with an α,β-unsaturated carbonyl in a 1,4-addition. [10] Some authors have broadened the definition of the Michael addition to essentially refer to any 1,4-addition reaction of α,β-unsaturated carbonyl compounds.
Alkenes are generally colorless non-polar compounds, somewhat similar to alkanes but more reactive. The first few members of the series are gases or liquids at room temperature. The simplest alkene, ethylene (C 2 H 4) (or "ethene" in the IUPAC nomenclature) is the organic compound produced on the largest scale industrially. [5]
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.