The pinacol rearrangement

Collins, Clair J.

doi:10.1039/qr9601400357

Cited by 86 publications

(32 citation statements)

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“…a 1,2-hydride shift to give the conjugate acid of benzophenone, should be considered. Such shifts occur with ease in many other systems (15). Over most of the acidity range examined, benzhydro1 is oxidized considerably faster than triphenylcarbinol and if the two pre-equilibrium steps are comparable, this would require a hydride shift to be faster than a phenyl shift.…”

Section: Mechanismmentioning

confidence: 99%

Chromic acid oxidation of aromatic alcohols

Stewart¹,

Banoo²

1969

Can. J. Chem.

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The mechanism of the chromic acid oxidation of di-and tri-aryl carbinols has been studied in 80 wt % acetic acid containing sulfuric acid. The reactions are cleanly second-order and give benzophenones in the case of the secondary alcohols and benzophenones plus phenols in the case of the tertiary alcohols. Electron-donating substituents in the tertiary alcohol appear predominantly in the phenol component and the rate-controlling step is believed to be a 1,2-aryl shift. The reaction constant for the migration is pf = -1.44 and that for the overall reaction is pf = -0.879. The presence of manganous ions does not alter these values although it lowers the overall rate of reaction. Although an analogous 1,Zhydride shift mechanism can be written for the oxidation of the secondary alcohols, there are enough points of difference between the oxidations of the secondary and tertiary systems to make this appear unlikely.

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Section: Mechanismmentioning

confidence: 99%

Chromic acid oxidation of aromatic alcohols

Stewart¹,

Banoo²

1969

Can. J. Chem.

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“…The pinacolic‐pinacolone rearrangement is known since the middle of the 19th century and used as an important tool for the formation of new skeletons, often applied for natural products or biomimemitics synthesis . This rearrangement constitutes one of the oldest transformations in carbocation chemistry . Its synthetic utility, various theoretical aspects, including mechanistic considerations, have been thoroughly discussed in different reviews .…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5][6][7][8][9][10][11] This rearrangement constitutes one of the oldest transformations in carbocation chemistry. [12][13][14][15] Its synthetic utility, various theoretical aspects, including mechanistic considerations, have been thoroughly discussed in different reviews. [16][17] Typically, the reaction has been reported using strong Brönsted acids, [18][19][20][21] Lewis acids [22][23][24] as well as solid-supported ones, [25][26][27][28][29][30][31][32] heteropolyacids, [33][34][35] ionic liquids [36] or crystals [37] or aminium salts.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Selectivity: Study of Solvent‐Free Acid‐Mediated Pinacolic‐Pinacolone Rearrangement under Microwave Irradiation

2018

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Here we report an efficient solvent‐free pinacolic‐pinacolone rearrangement using supported acids. Given a standard procedure (5 minutes microwave heating at 180 °C), changing the acid catalyst allow to reverse the selectivity of the reaction. The optimized conditions represent an efficient means by which pinacol‐pinacolone rearrangement can be carried out while avoiding the use of strong homogeneous Brönsted acids and extended reaction times. This neat reaction gave the products in high yield, purity and ease of recovery. Moreover, the catalyst can be reused on 10 runs without any loss of activity nor selectivity. As a consequence, that protocol can be referred as a green and efficient process for pinacol‐pinacolone rearrangement.

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“…With 97% acetic acid, the diol I gave the aldehyde I1 and a small quantity of 1,2-diacetoxy-1, 2-di-(P-methoxypheny1)-ethane (IV). By analogy with the mechanism proposed [5] [6] for rearrangement of other substituted vicinal diols, the following mechanism may be advanced to explain the conversion of the diol I to the aldehyde 11:…”

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confidence: 99%

“…the aldehyde I1 rearranged to the deoxybenzoin. The formation of the deoxybenzoin could apparently be due to an aldehyde-ketone rearrangement IS] [6].…”

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confidence: 99%

Pinacol‐Pinacolone Rearrangement of 1, 2‐Di‐(p‐methoxyphenyl)‐ethane‐1, 2‐diol and Bis‐(4‐methoxyphenyl)‐acetaldehyde in Acid Media

Tadros

Sakla

Awad

et al. 1972

Helvetica Chimica Acta

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Die Elcmentaranalysen wurden im mikroanalytischen Laboratorium der ETH Zurich (Leitung : W . Manser) ausgefuhrt. Die NMR.-Spektren wurden in unscrer Instrumentalabteilung (Leitung fur NMR.-Service : Prof. J . F . M . 0 t h ) aufgenommen. Die masscnspektroskopischen Analysen verdanlren wir Herrni PD Dr.Summary. l,Z-Di-(p-methoxyphenyl)-ethanc-l, 2-diol gave in acid media bis-(4-methoxy-pheny1)-acetaldehyde, 4,4'-dimethoxy-deoxybenzoin, and 1, 2-di-(p-methoxypheny1)-ethylenc oxide; their respective yields being influenced by a t least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period.Bis-(4-methoxyplienyl)-acetaldehyde rearranged to the deoxybcnzoin in boiling sulfuric (50 yo) or phosphoric (75%) acids ( w / w ) , and to two isomeric 1,2-diacetoxy-l, 2-di-(p-methoxypheny1)ethanes when it was heated with acetic anhydride.The mechanisms of these reactions are discussed.

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The pinacol rearrangement

Cited by 86 publications

References 0 publications

Chromic acid oxidation of aromatic alcohols

Chromic acid oxidation of aromatic alcohols

Tuning the Selectivity: Study of Solvent‐Free Acid‐Mediated Pinacolic‐Pinacolone Rearrangement under Microwave Irradiation

Pinacol‐Pinacolone Rearrangement of 1, 2‐Di‐(p‐methoxyphenyl)‐ethane‐1, 2‐diol and Bis‐(4‐methoxyphenyl)‐acetaldehyde in Acid Media

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