Aryl methyl ketones migration

In this reaction it is not the aryl group that migrates, as it does in the Wolff rearrangement (page 1090) on the contrary, the oxygen moves to the end of the chain and the carbon skeleton is unaffected. The reaction is not confined to aryl methyl ketones. For example, propiophenone gives 3-phenylpropion-amide 33... 

In a mechanistic study on the Lewis acid catalyzed addition of ethyl diazoacetate to ketones a similar profile of rearrangement to the 3-keto esters was observed (Scheme 9). In the same reaction with acetophenones, substitution on the benzene ring was found to only slightly affect the otherwise 90 10 preference for migration of aryl versus methyl. ... 

Murakami and coworkers reported a further use for this rhodium migration [80, 81]. Instead of protonolysis, they noticed that the aryl rhodium species after the vinylic to aryl migration is nucleophilic enough to attack an ester moiety in an intramolecular fashion to afford a cyclic ketone. Thus, an internal alkyne equipped with ester groups at a specific place was subjected to the rhodium-catalyzed hydroarylation conditions (Scheme 21). Indeed, the desired ketone was obtained in an 89% yield. Not only methyl esters can serve as acylation agents ethyl esters and isopropyl esters are also suitable substrates. 

Compound 157 has been used in a short synthesis of (/ )-ibuprofen methyl ester (161) [58] (Scheme 24). Acetalization of optically pure aryl ketone 159 under basic conditions produces hydroxy acetal 160 (74% ee), where the configuration at the asymmetric carbon is inverted. Treatment of 160 with sulfuryl chloride in pyridine at —50 °C causes facile 1,2-aryl migration and affords the target molecule 161 stereospecifically. 

Aryl epoxides undergo rearrangements to aldehydes and ketones in the presence of Lewis acid catalysts. For example, the cyclopentene oxide derivative 80 opens up to the more stable benzylic carbocation, which then provides the cyclopentanone derivative 82 via 1,2-methyl migration in 93% yield <01T815>. A similar rearrangement (83 84) has been shown to... 

This oxygenation reaction proceeds under milder conditions as compared to conventional methods. Despite the lower reactivities, VO(OR)3 and VO(acac>2 can be employed as an oxidant, although a stoichiomettic amount is required in each case. Use of a,p-unsaturated ketones leads the different reaction routes. 2-Cyclohexen-l-ones 54 undergo dehydrogenative aromatization to give the aryl alkyl ethers 55 [105]. More than 2 equiv. of VO(OR)Cl2 are required to complete the reaction, since the oxovanadium(V) compound is a one-electron oxidant. Isophorone is also oxidatively aromatized to the aryl ether 56 with the migration of the methyl group (Scheme 2.45). 

Treatment of [ C]methyl aryl ketones with thaUium(lll) nitrate in acidic methanol (McKillop rearrangement) or with ammonium polysulfide or sulfur and morpholine at elevated temperatures (Willgerodt-Kindler reaction) provides labeled arylacetic acid derivatives. In the first case the aryl group migrates from the carbonyl position into the former methyl position, so that the label is shifted by one position. For example (Figure 6.12), in the synthesis of [6- / C]porphobilinogen the pyrrole 22 was acetylated with... 

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