Esters rearrangement

Allylic ester rearrangement is catalyzed by both Pd(II) and Pd(0) compounds, but their catalyses are different mechanistically. Allylic rearrangement of allylic acetates takes place by the use of Pd(OAc>2-Ph3P [Pd(0)-phosphine] as a catalyst[492,493]. An equilibrium mixture of 796 and 797 in a ratio of 1.9 1.0 was obtained[494]. The Pd(0)-Ph3P-catalyzed rearrangement is explained by rr-allylpalladium complex formation[495]. 

Propionic acid, 2-bromo-3-(3-indolyl)-methyl ester rearrangement, 4, 279 Propionic acid, 3-(3,4-dimethyoxyphenyl)-dihydrocoumarin synthesis from, 3, 848 Propionic acid, indolyl-synthesis, 4, 232 Propionic acid, 3-(l-indolyl)-sodium salt pyrolysis, 4, 202 Propionic acid, 3-(3-indolyl)-intramolecular acylation, 4, 220, 221 Propionic acid, 3-phenoxy-chroman-4-one synthesis from, 3, 855 Propionic acid, 3-(3-phenylisoxazoI-5-yl)-bromination, 6, 25... 

A variant is represented by the benzilic ester rearrangement, where an alkoxide is used as nucleophile. The alkoxide should not be sensitive towards oxidation. The reaction product is the corresponding benzilic acid ester 5 ... 

Since the initially formed enol ester rearranges slowly to an imide,3 the yield depends on the rate at which the isoxazolium salt reacts, and that rate is increased by vigorous stirring. The reaction time for the activation step is approximately 8 minutes in nitromethane at 25° and approximately 1 hour in acetonitrile at 0°. In reactions performed with acetonitrile as the solvent, the checkers did not obtain complete solution. The reaction flask should be kept in a water bath to minimize heat transfer from the magnetic stirrer to the reaction mixture. 

The other fragmentation pathways are typical for diaryl sulfoxides "" . A corresponding ortho effect was found in chlorodiphenyl ethers and sulfides but not in sulfones (12) were the sulfinate ester rearrangements " and the consequent formation of the m/z 125 and m/z 159 ions suppress the other possible fragmentations of the molecular ions (equation 4). It is also noteworthy that the ratio [m/z 125] [m/z 159] increases with increasing distance between the chlorine and the sulfur (equation 4). 

Efremov and coworkers observed that electron-donating groups promote the sulfoxide-sulfonate ester rearrangement in the molecular ions of 2,4-dinitrophenyl... 

Pedersen and coworkers investigated the El mass spectra of several 2-hydroxyphenyl alkyl sulfones (39) and sulfoxides (Section II.B). The methyl derivative seemed to fragment only via sulfinate ester formation giving the primary product ions m/z 157 and 109 (equation 14). Obviously hydrogen bonding between the ortho hydroxyl and the sulfone sulfur makes the loss of CH3SO2 difficult in contrast to the situation in methyl phenyl sulfone. The sulfinate ester rearrangement is not important when R>Et in 39. 

The ester/alkyne rearrangement system can be extended by conjugation to involve a more distant site. The reaction of diethyl phosphorochloridate with 3-methylhex-4-yne-2-ene-l-ol leads to the vinylogous propargylic ester rearrangement as shown in Equation 4.39.176... 

An allylic phosphorus ester rearrangement to form a new C-P bond has been reported under photochemical conditions.179 Under irradiation in the presence of 9,10-dicyanoanthracene, an allylic phosphite ester undergoes rearrangement to form the corresponding allyl-icphosphonite ester (Equation 4.40). Benzophenone serves only poorly as a photosensitizer in this reaction. 

Sometimes the acetylenic ester rearranges to the corresponding allenic ester. For example, when the triethylamine salt of 3-chloro-2-ethoxycarbonyl-4-phenyl-2-hexenoic acid is refluxed in toluene, the allenic ester and acetylenic ester are obtained in a ratio of 3 7 (total yield 70%). There are alternative routes to cyclopropylpropiolic acids and esters, such as adding butyllithium to corresponding acetylenes and treating the product with carbon dioxide or methyl chloroformate. ... 

Claisen ortho ester rearrangement of propynyl alcohols of high enantiomeric purity gives the /S-allenylcarboxylic esters with diastereoselectivities of 90 10 up to 95 5110. 

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