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NBS will react with alkenes 1 in aqueous solvents to give bromohydrins 2. The preferred conditions are the portionwise addition of NBS to a solution of the alkene in 50% aqueous DMSO, DME, THF, or tert-butanol at 0 °C. [3] Formation of a bromonium ion and immediate attack by water gives strong Markovnikov addition and anti stereochemical ...
In the Goldfinger mechanism, the purpose of the NBS is simply to maintain a very low concentration of molecular bromine, while in the Bloomfield mechanism, its purpose is the generation of the initial radical used in the reaction, [11] which again can be quite a difficult process. [12]
Jacobsen's catalysts R = Alkyl, O-alkyl, O-trialkyl Best Jacobsen catalyst: R = t Bu Katsuki's catalysts R 1 = Aryl, substituted aryl R 2 = Aryl, Alkyl. The Jacobsen epoxidation, sometimes also referred to as Jacobsen-Katsuki epoxidation is a chemical reaction which allows enantioselective epoxidation of unfunctionalized alkyl- and aryl- substituted alkenes.
The mechanism of epoxidation with dioxiranes likely involves concerted oxygen transfer through a spiro transition state. As oxygen transfer occurs, the plane of the oxirane is perpendicular to and bisects the plane of the alkene pi system. The configuration of the alkene is maintained in the product, ruling out long-lived radical intermediates.
However, as is the case with the overall mechanism, the pathway of alkene approach is also debated. [8] One proposed substrate approach pathway - Note: Substrates are perpendicular to the plane of the catalyst. The ease with which Jacobsen's catalyst selectively epoxidizes cis-alkenes has been difficult to replicate with terminal and trans ...
Free-radical reactions depend on one or more relatively weak bonds in a reagent. Under reaction conditions (typically heat or light), some weak bonds homolyse into radicals, which then induce further decomposition in their compatriots before recombination. Different mechanisms typically apply to reagents without such a weak bond.
3. Traditional Wassail. Forget boring cider — wassail is the OG festive drink dating back to medieval England. Part of a tradition called “wassailing,” it was made to toast good health and ...
Studies investigating the mechanism of cobalt-catalyzed peroxidation of alkenes by Nojima and coworkers, [4] support the intermediacy of a metal hydride that reacts with the alkene directly to form a transient cobalt-alkyl bond. Homolysis generates a carbon centered radical that reacts directly with oxygen and is subsequently trapped by a ...