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To a cold (–78°) stirred solution of lithium diisopropylamide (1.4–1.5 mmol/mmol of ketone) in dry THF (4 mL/mmol of base) under an atmosphere of argon was added slowly a solution of n-butyl-trans-2-vinylcyclopropyl ketone (1.19 mmol) in dry THF (1 mL/mmol of ketone), and the resulting solution was stirred at –78° for 45 minutes.
The reaction can also be quenched with pyridine, which will scavenge ZnI 2 and excess reagents. [24] Methylation of heteroatoms is also observed in the Simmons–Smith reaction due to the electrophilicity of the zinc carbenoids. For example, the use of excess reagent for long reaction times almost always leads to the methylation of alcohols. [25]
Alternative Mechanism. The Corey-Winter olefination is a stereospecific reaction: [1] a trans-diol gives a trans-alkene, while a cis-diol gives a cis-alkene as the product. For instance, cis- and trans-1,2-cyclodecanediol gives the respective cis- and trans-cyclodecene.
1,2-Dibromoethylene, also known as 1,2-dibromoethene and acetylene dibromide, is a dihalogenated unsaturated compound with one bromine on each of the two carbon atoms. There are two isomers of this compound, cis and trans .
Although the mechanisms of each of these reactions differ somewhat, in each case the chiral catalyst or reagent must be involved in the enantio determining conjugate addition step. Cis-epoxides are difficult to access using nucleophilic epoxidation methods. Nearly all nucleophilic epoxidations of cis olefins afford trans epoxides.
[1] Diastereoselective epoxidation may be achieved through the use of alkene starting materials with diastereotopic faces. When racemic 3-isopropylcyclohexene was subjected to DMD oxidation, the trans epoxide, which resulted from attack on the less hindered face of the double bond, was the major product. [1]
[1] The vast majority of reagents are monosubstituted at the ylide carbon (either R 1 or R 2 as hydrogen). Disubstituted reagents are much rarer but have been described: [1] If the ylide carbon is substituted with an electron-withdrawing group (EWG), the reagent is referred to as a stabilized ylide. These, similarly to sulfoxonium reagents ...
The Prilezhaev reaction, also known as the Prileschajew reaction or Prilezhaev epoxidation, is the chemical reaction of an alkene with a peroxy acid to form epoxides. [1] It is named after Nikolai Prilezhaev , who first reported this reaction in 1909. [ 2 ]