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The pinacol–pinacolone rearrangement is a method for converting a 1,2-diol to a carbonyl compound in organic chemistry. The 1,2-rearrangement takes place under acidic conditions. The name of the rearrangement reaction comes from the rearrangement of pinacol to pinacolone .
The pinacol coupling can be followed up by a pinacol rearrangement. A related reaction is the McMurry reaction , which uses titanium(III) chloride or titanium(IV) chloride in conjunction with a reducing agent for the formation of the metal-diol complex, and which takes place with an additional deoxygenation reaction step in order to provide an ...
Most famously, at least in the classroom, pinacolone arises by the pinacol rearrangement, which occurs by protonation of pinacol (2,3-dimethylbutane-2,3-diol). [4] Industrially pinacolone is made by the hydrolysis of 4,4,5-trimethyl-1,3-dioxane, which is the product of isoprene and formaldehyde via the Prins reaction.
Spiro compounds are often prepared by diverse rearrangement reactions. For example, the pinacol-pinacolone rearrangement is illustrated below. [3]: 985 is employed in the preparation of aspiro[4.5]decane. [12]]. The synthesis of a spiro-keto compound form a symmetrical diol
In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. [1] Often a substituent moves from one atom to another atom in the same molecule, hence these reactions are usually intramolecular.
Pinacol is a branched alcohol which finds use in organic syntheses. It is a diol that has hydroxyl groups on vicinal carbon atoms. A white solid that melts just above room temperature, pinacol is notable for undergoing the pinacol rearrangement in the presence of acid and for being the namesake of the pinacol coupling reaction .
In the pinacol rearrangement, the order of migratory aptitude has not been determined unambiguously, [2] but some trends have been determined. For example, relative migratory aptitudes for alkyl substituents is Hydride >C(CH 3) 3 > C 2 H 5 > phenyl > CH 3. [2] More bulky groups have more tendency to migrate.
A common migration introduction of carbon is a pinacol rearrangement. [1] While this reaction refers specifically to a vicinal dihydroxide rearrangement, there are other pinacol type rearrangements that proceed through the same general mechanism such as the Tiffeneau–Demjanov rearrangement.