Retroaldol condensation

Formulate this reaction as a reversal of an aldol condensation (retroaldol condensation). ... 

The formation of pyrroles 54 and 57 is likely to be a result of decomposition of the oximes 55 and 59 in the form of dianion by analogy with retroaldol condensation (Scheme 33). As far as the formation of pyrrole 57 (Schemes 28 and 29) is concerned, this seems to result from -elimination of water and vinyl alcohol molecules from the oximes 55 and 58 respectively or from the corresponding intermediate 2-hydroxy(vinyloxy)propyl-1-vinylpyrroles. 

I) is a /(-hydroxyketone. Loss of a proton from the —OH affords an alkoxide (IV) that undergoes a retroaldol condensation by cleavage of the Ca—bond. 

Redox equations, balancing, 265 Reduction of aromatic compounds, 200 Reductive amination, 404 Reductive hydroboration, 95 Reformatsky reaction, 321 Regioselective reactions, 97 Reimer-Tiemann reaction, 438 Resonance, 23 in benzene, 192 energy, 24 structures, 29 Resorcinol, 327, 432 Retroaldol condensation, 399 Ring activation, 2(fiff Robinson inaction, 398 Rosenmund reduction, 306... 

These conditions gave excellent selectivity for an external methyl dienoate in the presence of a more hindered internal dienoate during a synthesis of the complex macrolide swinholide. These conditions are also mild enough to prevent retroaldol condensation during ester hydrolysis. In general, the barium salts may also be removed by precipitation with CO2 to form BaCO, which is readily filtered off, a method that is especially useful for water-soluble substrates. 

Stilbenes are claimed to exist in lignin-containing pnlps. One mechanism for their formation is the retroaldol condensation of (3-1 and (3-5 lignin structures in the presence of alkali (see the Alkali Darkening section). 

The general class of enzymes catalyzing aldol or retroaldol condensation reactions are the aldolases (Table VI) (156-161). In principle, there are four possible stereochemical routes to product depending on whether C-C bond formation involves retention or inversion of configuration at the methyl or methylene carbon atom a to the ketonic carbonyl (Eq. (30)] ... 

If the electrophile removed from the initially formed imine is an aldehyde then a retroaldol condensation occurs. For example, serine may be converted to glycine by this mechanism. 

This is the mechanism of catalysis by aldolases which occur in plant and animal tissues (lysine aldolases or class I aldolases). A second group of these enzymes often produced by microorganisms contains a metal ion (metallo-aldolases). This group is involved in accelerating retroaldol condensations through electrophihc reactions with carbonyl groups ... 

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