Rearrangement reactions pinacol

The pinacol rearrangement reaction is of limited synthetic importance although it can be a useful alternative to the standard methods for synthesis of aldehydes and ketones." Especially in the synthesis of ketones with special substitution pattern—e.g. a spiro ketone like 5—the pinacol rearrangement demonstrates its synthetic potential ... 

The required vicinal diols are in general accessible by standard methods. Pinacol itself can be obtained by dimerization of acetone. For the rearrangement reaction concentrated or dilute sulfuric acid is often used as catalyst. 

A vicinal diol 1, when treated with a catalytic amount of acid, can rearrange to give an aldehyde or ketone 3 by migration of an alkyl or aryl group. The prototype of this reaction is the rearrangement of pinacol (R = r2 = = r4 = CH3) to... 

The above-described rearrangement reactions are not the only ones presented within this book. In addition to electrocyclic rearrangements, some rearrangements dependent upon ionic mechanisms were presented. These include the pinacol rearrangement... 

Semipinacol rearrangements are pinacol reactions with no choice about which way to go... 

Many common rearrangement reactions are related to the rearrangement of 1,2-dihydrojqr compounds to carbonyl compounds. Often these reactions are called pinacol rearrangements, because one of the first examples was the transformation of pinacol to pinacolone ... 

Moriyoshi, T., Tamura, K. Effects of pressure on organic reactions. II. Acid-catalyzed rearrangement of pinacol. Rev. Phys. Chem. Japan 1970,40, 48-58. 

A polymeric pinacol,poly[3-methyl-2-(4-vinylphenyl)-2,3-butanediol],has been prepared by radical polymerization of the styrenic diol monomer and shown to be cleanly and quantitatively converted to a non-conjugated ketone in the solid state by reaction with a photochemically-generated acid [151,348, 350]. The rearrangement reaction can be readily monitored by IR spectroscopy as the disappearance of the hydroxyl OH absorption is accompanied by appearance of a new ketone carbonyl absorption (Fig. 116). Since a polar alcohol (isopropanol) dissolves the polar diol polymer in the unexposed regions but cannot dissolve the less polar ketone polymer produced in the exposed regions, the resist functions as a negative system with alcohol as a developer. The diol polymer is stable thermally to 225 °C in the absence of acid. 

Perhaps the quintessential cationic rearrangement reaction used for synthesis is the Pinacol rearrangement. Fittig was the first to discover that treatment of 2,3-dimethyl-2,3-butanediol (118) with sulfuric acid... 

For another classical problem of nucleophilic aliphatic substitution and rearrangement, namely pinacolic deaminations and rearrangements, the use of cyclohexane derivatives with a tert-hvXyX group instead of open-chain alkane derivatives was very helpful. The stereochemistry of these reactions was studied first by Bernstein and Whitmore (1939). Specific labeling with used first by Collins and his coworkers (Benjamin et al., 1957), helped significantly to elucidate the complex pathway of pinacolic deamination. Even summarizing the results would take far too much space here. 

A pinacol-pinacolone rearrangement reaction involving polarity switch of a polar to a nonpolar functional group in a resist polymer has been exploited in... 

Efficient preparation of 2,3-diarylbenzo[ft]thiophenes (475) is accomplished in two ways starting from thioisatins (474) (Scheme 98) <83TL3381>, A series of reactions, that is, Grignard reaction, pinacol rearrangement, hydride reduction, and acid-catalyzed rearrangement, converts (474) to thiophenes (475). Another series of reactions, Friedel-Crafts reaction, hydride reduction, and acid-catalyzed rearrangement, also convert (474) to (475). 

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