Pinacol acid-catalyzed

Selective hydroxylation with osmium tetroxide (one equivalent in ether-pyridine at 0 ) converts (27) to a solid mixture of stereoisomeric diols (28a) which can be converted to the corresponding secondary monotoluene-sulfonate (28b) by treatment with /7-toluenesulfonyl chloride in methylene dichloride-pyridine and then by pinacol rearrangement in tetrahydrofuran-lithium perchlorate -calcium carbonate into the unconjugated cyclohepte-none (29) in 41-48 % over-all yield from (27). Mild acid-catalyzed hydrolysis of the ketal-ketone (29) removes the ketal more drastic conditions by heating at 100° in 2 hydrochloric acid for 24 hr gives the conjugated diketone (30). 

Rearrangement, acid-catalyzed, of cyclohexanone diallyl acetal to 2-allylcyclohexanone, 42,14 of e do-tetrahydrocyclopentadiene to adamantane, 42,9 pinacol, of 1,2-indanediol, 41, 53... 

A reaction that follows this pattern is the acid-catalyzed conversion of diols to ketones, which is known as the pinacol rearrangement.60 The classic example of this reaction is the conversion of 2,3-dimethylbutane-2,3-diol(pinacol) to methyl /-butyl ketone (pinacolone).61... 

Sasidharan et al. (258) reported the formation of pinacols from alkenes catalyzed by various titanosilicates. Aluminum-free Ti-beta exhibited better activity and pinacol selectivity than TS-1, TS-2, Ti-MCM-22, or mesoporous Ti-MCM-41 (Table XLVIII). The side products included the pinacolone, alcohol, and oligomers. The epoxide was the initial product, which underwent acid-catalyzed nucleophilic ring-opening by H2Q molecules to give the pinacol (Scheme 25). 

Acid-catalyzed rearrangement of vicinyl diols (pinacols) to carbonyl compounds. 

The preparation of 620, a tricyclic intermediate suited for elaboration into quadrone, has been reported by Monti and Dean Following introduction of the proper C5, stereochemistry by alkylation of 618 under kinetically controlled conditions, diketone 619 was subjected to acid-catalyzed rearrangement. After functional group manipulation, a tandem intramolecular aldol-pinacol rearrangement gave 620. 

Reaction type 6C (Table 10-1) occurs during the biosynthesis of leucine and valine (Fig. 24-17). The rearrangement is often compared with the nonenzy-matic acid-catalyzed pinacol-pinacolone rearrangement in which a similar shift of an alkyl group takes place (Eq. 13-57). The enzyme-catalyzed rearrangement... 

Many carbonyl compounds can be synthesized by acid-catalyzed rearrangements of 1,2-diols (a type of reaction often called the pinacol-pinacolone rearrangement). 

In the conversion that gave its name to this reaction, the acid-catalyzed elimination of water from pinacol give s r-butyl methyl ketone. 

Hydride Reduction of a Carbonyl Group 454 Reaction of a Tertiary Alcohol with HBr(S[ 1) 480 Reaction of a Primary Alcohol with HBr (SN2) 480 Reaction of Alcohols with PBr3 485 (Review) Acid-Catalyzed Dehydration of an Alcohol 487 The Pinacol Rearrangement 495 Cleavage of an Ether by HBr or HI 639 Acid-Catalyzed Opening of Epoxides in Water 649 Acid-Catalyzed Opening of an Epoxide in an Alcohol Solution 650... 

Problem 28.9 The following reactions have all been found to yield a mixture of pinacol and pinacolone, and in the same proportions treatment of 3-amino-2,3-dimethyl-2-butanol with nitrous acid treatment of 3-chloro-2,3-dimethyl-2-butanol with aqueous silver ion and acid-catalyzed hydrolysis of the epoxide of 2,3-dimethyl-2-butene. What does this finding indicate about the mechanism of the pinacol rearrangement ... 

Sugihara, Y., limura, S., Nakayama, J. / za-pinacol rearrangement acid-catalyzed rearrangement of aziridines to imines. Chem. Commun. 2002, 134-135. 

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 similar stereoselectivity has been described for the Lewis acid catalyzed pinacol rearrangement of vinyl-24 and cyclopropyl-substituLed25 hydroxysulfonates 16 (via mesylation) and 17. Of note is a dramatic rate enhancement observed for the [1,2] rearrangement of silyl-substituted substrates 16, an observation consistent with the well-documented ability of silicon substituents to stabilize / -carbocations. 

Fig. 116 IR spectra of polymeric pinacol demonstrating its thermal stability and acid-catalyzed rearrangement to ketone [151]...

The idea of solid-phase acid-catalyzed processes was originally developed by Toda et al. [46,47]. The pinacol rearrangement of aryl-substituted secondary and tertiary diols in the presence of solid p-toluenesulfonic acid (333 K) and trichloroacetic acid (293 K) was found to proceed faster and more selectively than in solution (batch reactor) [46]. 

Chemically amplified negative resists based on acid-catalyzed pinacol rearrangement... 

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