2.3.2 Crossed-Condensation
Similar to base-catalyzed reactions, crossed reactions between two enolizable carbonyl compounds may result in a mixture of four products. However, if only one of the two compounds can enolize and the other has the more reactive carbonyl group, a single product may then be formed. For example, the reaction of enolizable acetophenone with non-enolizable more reactive benzaldehyde can give single product in good yield.
2.3.3 Reactions between Ketones and Acid Chlorides or Anhydrides
Ketones react with compounds having more reactive carbonyl groups such as acid chloride or anhydrides. For example, the reaction of acetone with Ac2O in presence of BF3 gives 2,4-pentanedione.
2.3.4 Reactions of 2-Methylpyridine and Analogue
Compounds such as 2- and 4-methylpyridines, and 2- and 4-methylquinolines react with aldehydes in presence of ZnCl2 which catalyzes their conversion into the nitrogen-analogue of an enol. For example, 2-methylpyridine proceeds reaction with benzaldehyde in presence of ZnCl2 .
