Ketone rearrangement

Neber oxime tosylate-amino ketone rearrangement... 

The subjects of this section are two reactions that do not actually involve carbo-cation intermediates. They do, however, result in carbon to carbon rearrangements that are structurally similar to the pinacol rearrangement. In both reactions cyclic intermediates are formed, at least under some circumstances. In the Favorskii rearrangement, an a-halo ketone rearranges to a carboxylic acid or ester. In the Ramberg-Backlund reaction, an a-halo sulfone gives an alkene. 

An application involving the use of a polystyrene-immobilized aluminum(III) chloride for a ketone-ketone rearrangement has been presented by Gopalakrishnan and coworkers [144]. 

E,E)-a,P Y,5-Drenones.2 Aryl a,(3-alkynyl ketones rearrange in the presence of this ruthenium catalyst in refluxing toluene to conjugated (E,E)-dienones in 75-85% yield. A similar rearrangement with alkyl a,(i-alkynyl ketones proceeds less readily. 

The suitably protected amino acid is activated as the mixed anhydride and treated with diazomethane to produce the corresponding diazo ketone. Rearrangement in the presence of water furnishes the p-amino acid. Diazomethane contains varying amounts of water, which is able to hydrolyze the activated amino acid. This leads to subsequent methylation by diazomethane to form the methyl ester as a side product. This cannot easily be removed from the diazo ketone, but can be separated during work-up of the homologated amino acids. 

Cycloadduct 212 is converted into the dihydrobenzofuran 213 when treated with boron trifluoride diethyl etherate in good yield <2000JA8155>. The formation of the dihydrobenzofuran proceeds by an initial ring opening followed by a subsequent dehydration and acid-catalyzed cyclopropyl ketone rearrangement (Equation 142). 

This is sufficiently reactive to attack the C—H bond forming the five-coordinate car-bocation 16 to give protonated pivalaldehyde (Scheme 7.2). The latter undergoes the aldehyde-ketone rearrangement to yield the corresponding branched ketone. 

The epoxide-ketone rearrangement is not limited to polyfluorooxiranes. Michel and Schlosser have studied the isomerization of 2-fluorooxiranes to oc-fluoro ketones by the action of triethylamine trishydrofluoride.47 Thus, 2-substituted 2-fluorooxiranes 10 isomerize re-giosclectively to fluoromethyl ketones 11 when heated at 125 C. 

Ketone—ketone rearrangements using polymer-supported MCI 3... 

Gopalakrishnan, G., Kasinath, V. and Singh, N.D.P., Microwave-assisted ketone-ketone rearrangement an improved synthesis of 3-(4-alkoxyphenyl)-3-methylbutan-2-ones, Org. Lett., 2002, 4, 781. 

The question remains Is the formation of 133 or its destruction ratedetermining Experiment indicates that rearrangement is concerted and that in the oxidation of most ketones rearrangement is rate-determining. 

Propose a mechanism for the reaction in Equation 10, an example of the aldehyde-ketone rearrangement. 

Tertiary allylic alcohols form a chromate ester that, as it lacks a hydrogen on a to the alcohol, instead of suffering a normal oxidation to ketone rearranges to an enone. This transformation, which can be brought about by other chromium-based reagents, is normally carried out with PCC when it is purposefully sought at (see page 55). 

Lewis Acid-Catalysed Cyclopropyl Ketone Rearrangement... 

Rearrangement of a-phenylselenenyl ketones. Various a-phenylselenenyl ketones rearrange in the presence of 0.5 equiv. of LDA and HMPT to a -phenylselenenyl ketones, apparently by an intermolecular process. This rearrangement is observed particularly with substrates substituted by alkyl groups in the a- and /1-positions. The reaction provides a route to a, // -unsaturated ketones.9... 

Rearrangement of (a-methyldiphenylsilyl)alkyl ketones.1 These a-silyl ketones rearrange thermally to a mixture of (Z)- and (E)-enol silyl ethers. However, rearrangement in acetonitrile results in only the (Z)-enol silyl ethers (>99 1). These enol silyl ethers are useful precursors to (Z)-lithium enolates. 

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