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a Diels-Alder reaction. Alkenes add to dienes to give cyclohexenes. This conversion is an example of a Diels-Alder reaction. Such reaction proceed with retention of stereochemistry. The rates are sensitive to electron-withdrawing or electron-donating substituents. When irradiated by UV-light, alkenes dimerize to give cyclobutanes. [20]
The reaction is a two-stage process, in which first the alkene is reacted with dichlorocarbene or dibromocarbene to form a dihalocyclopropane. This intermediate is then reacted with a reducing metal, such as sodium or magnesium, or with an organolithium reagent .
The periselectivity of a particular reaction depends on the structure of both the ketene and the substrate. Although the reaction is predominantly used to form four-membered rings, a limited number of substrates undergo [3+2] or [4+2] reactions with ketenes. Examples of all three modes of cycloaddition are discussed in this section.
The Woodward cis-hydroxylation (also known as the Woodward reaction) is the chemical reaction of alkenes with iodine and silver acetate in wet acetic acid to form cis-diols. [1] [2] (conversion of olefin into cis-diol) The reaction is named after its discoverer, Robert Burns Woodward. The Woodward cis-hydroxylation
Cyclization reactions, or intramolecular addition reactions, can be used to form cycloalkenes. These reactions primarily form cyclopentenones, a cycloalkene that contains two functional groups: the cyclopentene and a ketone group. [12] However, other cycloalkenes, such as Cyclooctatetraene, can be formed as a result of this reaction. [11]
The McMurry reaction of benzophenone. The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to form an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent. The reaction is named after its co-discoverer, John E. McMurry.
In organic chemistry, an addition reaction is an organic reaction in which two or more molecules combine to form a larger molecule called the adduct. [1] [2] An addition reaction is limited to chemical compounds that have multiple bonds. Examples include a molecule with a carbon–carbon double bond (an alkene) or a triple bond (an alkyne).
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]