Gold(III)-mediated aldol condensations provide efficient access to nitrogen heterocycles
Herbert Waldmann1, Galla V Karunakar, Kamal Kumar
1Max-Planck-Institut Für Molekulare Physiologie, Abteilung Chemische Biologie, Dortmund, Germany. herbert.waldmann@mpi-dortmund.mpg.de
Organic Letters
|May 9, 2008
Abstract:
Quinolines, dihydroquinolines, and aza-xanthones can be synthesized efficiently and under mild reaction conditions by means of a reaction sequence employing Au(III)-catalyzed aldol reactions as the key step.
Related Concept Videos
Aldol Condensation with β-Diesters: Knoevenagel Condensation
The Knoevenagel condensation is an aldol-type reaction involving the condensation of aldehydes or ketones with active methylene compounds such as β-diesters to produce substituted olefins.
C–C Bond Formation: Aldol Condensation Overview
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
Aldol Condensation vs Claisen Condensation
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.
Crossed Aldol Reactions: Overview
Crossed aldol addition is the reaction between two different carbonyl compounds under acidic or basic conditions. Here, both the carbonyl compounds function as nucleophiles and electrophiles. As shown in Figure 1, such a reaction yields a mixture of products, two of which are formed via self-condensation, while the remaining two are formed via crossed-condensation. Without adjustment, the reaction's usefulness in organic chemistry is decreased.
Acid-Catalyzed Aldol Addition Reaction
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
Intramolecular Aldol Reaction
Intramolecular aldol reaction occurs in dicarbonyl compounds such as dialdehydes, diketones, and keto-aldehydes. The dicarbonyl compounds possess more than one nucleophilic ⍺ carbon for the base to deprotonate and form the enolates. For example, in symmetrical diketones, there are four ⍺ carbons. Hence, four types of enolates are possible when treated with a base. However, since the molecule is symmetrical, the enolates formed on either side of one carbonyl group are equivalent to those formed...


