Aryl ketones stereospecific

Thus the triplet states of the two diastereomers react to yield different product distributions although this effect is far less marked for the triplet than for the singlet reaction, which is essentially stereospecific. The singlet reaction could be either concerted or due to an extremely shortlived biradical. Since the product distributions of the triple reaction of these two diastereomers are different, it is clear that cleavage must occur before complete equilibration. Thus the lifetime of the aliphatic ketone derived biradical must be considerably shorter than the corresponding biradical derived from an aryl ketone. 

One of the best known reactions of dialkyl cadmium compounds is that with acyl halides which results in the formation of ketones. The reactions of (CF3)2Cd glyme with CH, COBr and C6HhCOC1 were the third class of reactions of the trifluoromethylating reagent examined. However, the mixed trifluoromethylalkyl or -aryl ketones were not observed. The organic products obtained were the acyl fluorides (95% yield) along with difluorocarbene. The latter could be stereospecifically trapped at temperatures as low as -78°C. The addition of either lithium or magnesium halides to the reaction mixture did not affect the outcome (106). 

In an industrial asymmetric synthesis en route to the antiinflammatory agent naproxen, the dimethyl L-tartrate acetals of ethyl aryl ketones are brominated in high yield and selectivity to give the corresponding a-bromo derivatives. Subsequent stereospecific Ag -promoted 1,2-aryl migration provides the 2-alkyl-2-arylacetic acid after hydrolysis of the tartrate auxiliary, which is recovered (e.g. eq 4). 

Ketones. Condensations between the phosphonium salt (23) and alkyl aryl ketones in the presence of methylsulphinylmethanide ion lead to mixtures of (Z)-stilbenes and ( )-styrenes in stereospecific reactions resulting from dichotomous ylide formation (Scheme 2). The authors have shown that this unusual behaviour is due to the... 

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. 

Trimethylsilylation of enolizable carbonyl compounds and alcohols has also been accomplished by the fluoride ion promoted reaction with hexamethyldisilane and ethyl trimethylsilylacetate [48, 49], with high stereospecificity giving Z-enol ethers from ketones [50]. l-Trimethylsilyl-(l-trimethylsilyloxy)alkanes, produced from the reaction of aldehydes with hexamethyldisilane, undergo acid-catalysed hydrolysis during work up to yield the trimethylsilylcarbinols [51]. In the case of aryl aldehydes, the initially formed trimethylsiloxy carbanion produces the pinacol (Scheme 3.1). 

Since 1,4 addition of a variety of appropriate aryl caibanions to 36 failed, an intramolecular version of the Heck reaction was examined. With this end in view, the ketone 36 was reduced stereospecifically to the corresponding allyl alcohol which was then protected as its p-methoxybenzyl ether 37. The amine, obtained on reduction of the azide 37, was condensed with 6-bromopiperonylic acid to furnish the amide 38. 

Asymmetricpinacol-type rearrangement. Oiiral P-mesyloxy tertiary alcohols undergo a stereospecific pinacol-type rearrangement in the presence of triethylaluminum (excess) to furnish optically pure a-aryl or a-vinyl ketones (equation I). The reaction is particularly... 

Multiple intramolecular ring closures of aryl-substituted unsaturated long chain alcohols, acids, acid chlorides and ethers in the presence of Friedel-Crafts catalysts have been extensively employed to synthesize polynuclear hydroaromatic hydrocarbons and polycyclic ketones. This is illustrated by two examples shown in equations (112) and (113). The application of stereospecific cycloalkylations in approaching the synthesis of complex organic molecules has been reviewed by Barclay. ... 

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