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Organic Lab Reactions 192

Organic Lab Reactions 192 - CH 3_COCHa ~ XXVI However with...

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CONDENSATION 187 carry out these reductions with higher-boiling solvents. There are some indications that certain sterically hindered ketones may be resistant to aluminum isopropoxide reduction, but this is far from general. In the event of apparent failure of the method, it should be noted that other procedures, such as catalytic hydrogenation, often can be applied suc- cessfully. 0 0 ROOC CH CH 3 XXIV CH 3 Side XXV Reactions Several different types of side reactions have been observed during aluminum isopropoxide reductions. These, however, are encountered only occasionally and usually are not a source of difficulty. Condensation. Although aluminum alkoxides are effective in bring- ing about the mesityl oxide type condensation of ketones, as, for example, in the formation of dypnone (XXVII) from acetophenone (XXVI), 26 aluminum isopropoxide rarely induces this reaction to any significant degree in the reduction of ketones.
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Unformatted text preview: CH 3 \_COCHa / ~ \ XXVI However, with cyplopentanone only a 33% yield of cyclopentanol was obtained, the remainder of the material probably having undergone the above-mentioned condensation. 6 As no appreciable condensation of this type occurs if dilute solution (approximately 0.05 molar) is used, 10 it seems possible that dilution may improve the yields with particularly sensitive ketones such as cyclopentanone. With aldehydes, side reactions become more important. Aldol con-densations often are possible not only between two molecules of the aldehyde but also between the aldehyde and acetone. The yields are often lower in the reduction of aldehydes if the acetone is not removed as it is formed. 13 Higher temperatures, for example, that of boiling 28 Wayne and Adkins, J. Am. Chem. Soc , 62, 3401 (1940)....
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