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The reaction is named after pinacol (also known as 2,3-dimethyl-2,3-butanediol or tetramethylethylene glycol), which is the product of this reaction when done with acetone as reagent. The reaction is usually a homocoupling but intramolecular cross-coupling reactions are also possible. Pinacol was discovered by Wilhelm Rudolph Fittig in 1859.
Pinacol type rearrangements are often used for this type of contraction. [20] Like the expansion reaction this proceeds with an electron donating group aiding in the migration. Contraction reactions of one ring can be coupled with an expansion of another to give an unequal bicycle from equally sized fused ring.
The reaction product he obtained instead he called paraceton which he believed to be an acetone dimer. In his second publication in 1860 he reacted paraceton with sulfuric acid (the actual pinacol rearrangement). Again Fittig was unable to assign a molecular structure to the reaction product which he assumed to be another isomer or a polymer.
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 Baeyer-Villiger reaction, the more substituted group, in general, migrates. [3] 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]
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
Ambiguity effect; Assembly bonus effect; Audience effect; Baader–Meinhof effect; Barnum effect; Bezold effect; Birthday-number effect; Boomerang effect; Bouba/kiki effect
Other key reactions encountered in this synthesis are a pinacol coupling and a Reformatskii reaction. In terms of raw materials the C20 framework is built up from L-serine (C3), isobutyric acid (C4), glycolic acid (C2), methyl bromide (C1), methyl iodide (C1), 2,3-dibromopropene (C3), acetic acid (C2) and homoallyl bromide (C4).