Meyer-Schuster acidic rearrangement

The products from the acid-catalyzed hydration of a-tertiary alcohols 30 (Meyer-Schuster and Rupe rearrangements) are formed via the mesomeric propargyl-allenyl cation (equation 9) and have been extensively investigated28. 

When 2-ethynyl-2-hydroxyadamantane (31) was treated with 95% formic acid or dilute sulfuric acid only a Meyer-Schuster rearrangement took place to give 95% of 2-(formylmethylene)adamantane (32) (equation 10). No Rupe rearrangement took place29. 

Regarding the first problem, the most elemental treatment consists of focusing on a few points on the gas-phase potential energy hypersurface, namely, the reactants, transition state structures and products. As an example, we will mention the work [35,36] that was done on the Meyer-Schuster reaction, an acid catalyzed rearrangement of a-acetylenic secondary and tertiary alcohols to a.p-unsaturatcd carbonyl compounds, in which the solvent plays an active role. This reaction comprises four steps. In the first, a rapid protonation takes place at the hydroxyl group. The second, which is the rate limiting step, is an apparent 1, 3-shift of the protonated hydroxyl group from carbon Ci to carbon C3. The third step is presumably a rapid allenol deprotonation, followed by a keto-enol equilibrium that leads to the final product. 

Acid-catalyzed rearrangement of tertiary a-acetylenic (terminal) alcohols, leading to the formation of a,(3-unsaturated ketones rather than the corresponding a,(3-unsaturated aldehydes. Cf. Meyer-Schuster rearrangement. 

Finally, the synthesis is completed by using the Meyer-Schuster rearrangement of the Aren-van Dorp synthesis on enone acetal 152. Treatment of 152 with lithium etoxyacetilide in THF gives an unstable tertiary allylic-propargylic alcohol that, when dissolved in methanol with a catalytic quantity of sulphuric acid produces 63 and its epimer 98 in a proportion of 7 3, respectively, in 42% yield. 

Meyer-Schuster rearrangement. Acid catalyzed rearrangement of secondary and tertiary a-acetylenic alcohols to ,(i-unsaturated carbonyl compounds aldehydes when the acetylenic group is terminal, ketones when it is internal. 

MEYER - SCHUSTER Propargyl alcohol rearrangement Acid catalyzed rearrangement of acetylenic alcohols into a.0-unsaturated carbonyl derivatives. 

Meyer-Schuster rearrangement. Ammonium vanadate, diphenylsilanedio), and an alkanedicarboxylic acid constitute an efficient catalytic system for the conversion of propargyl alcohols to a,/3-unsaturated aldehydes. 

Raphael, the iodoaromatic (227) is first coupled with the acetylenic alcohol (228) in the presence of Pd° leading to the central intermediate (229). Meyer-Schuster rearrangement of (229) in the presence of methane sulphonic acid then gave rise to (231) presumably via the initially formed ketone (230). Reduction of (231) followed by dehydration next led to (232), which was elaborated to virantmycin, via epoxidation, reduction, deprotection, treatment with thionyl chloride, and finally ester hydrolysis. 

One of the first industrial muscone syntheses stems from work at BASF. [182] Analogous to the synthesis of exaltone, cyclododecanone is converted, by reaction with but-3-yn-2-ol, into a diol, which is further transformed by a Meyer-Schuster rearrangement and Nazarov cyclisation into a methyl-substituted bicycle. A very short route to the same product was described by Mitsui Petrochemical Industries a few years later this involved the direct conversion of cy-clododecene with crotonic acid in the presence of polyphosphoric acid, and resulted in a remarkable yield of 54 %. [183]... 

Tri-n-propyl vanadate I triphenylsilanoU benzoic acid a,/ - thylenealdehydes from 2-ethynylalcohols Meyer-Schuster rearrangement... 

Titanium tetra-n-butoxide j cuprous chloride jp-toluic acid a,p-Ethyleneoxo compds. ifrom 2-acetylenealcohols Meyer-Schuster rearrangement... 

Meyer-Schuster rearrangements of secondary and tertiary propargylic alcohols occur readily with PPh3AuNTf2, in the presence of 4-methoxyphenylboronic acid or 1 equiv. of methanol to give enones with high selectivity for the -alkene (Scheme 117). ... 

Although a variety of acid catalysts are employed in the Meyer-Schuster and Rupe rearrangements, formic acid is commonly used to effect the respective transformations. ... 

The synthetic practicality of the Meyer-Schuster rearrangement was demonstrated in the synthesis of ( )-virantmycin, a metabolite of Streptomyces nitrosporeus, which has been shown to possess antiviral activity. When the attempted conversion of 17 to 19 via a hydrogenation/cyclization sequence was unsuccessful, an alternate pathway utilizing the Meyer-Schuster reaction was explored. Treatment of 17 with acid was presumed to give the a,P-unsaturated ketone which underwent a spontaneous Michael reaction to give 18. Reduction of the resulting ketone 18 was followed by dehydration to provide 19. 

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