Aldol Dieckmann condensation

In a more recent publication the same research group described a Cu(OTF)2/(POEt)3-catalyzed two-component Michael/aldol protocol of 2-112 and ZnEt2 leading to annulated cyclopentanols [46]. They showed that the enolate formed in the 1,4-addition can be trapped not only by a keto moiety, but also by an ester (Dieckmann condensation) or a nitrile functionality present in the molecule. Thus, as depicted in Scheme 2.26, there is a broad product variety. Starting from 2-112, compounds of type 2-114, 2-115 and 2-116 can be obtained via the enolate 2-113. 

CLAISEN - GEUTER - DIECKMANN Ester condensation Synthesis o( open chain or cyclic p keloesters by aldol type condensation... 

Original Synthesis. The first attempted synthesis of 5 -biotin in 1945 afforded racemic biotin (Fig. 1). In this synthetic pathway, L-cysteine [52-90-4] (2) was converted to the methyl ester [5472-74-2] (3). An intramolecular Dieckmann condensation, during which stereochemical integrity was lost, was foUowed by decarboxylation to afford the thiophanone [57752-72-4] (4). Aldol condensation of the thiophanone with the aldehyde ester [6026-86-4]... 

In an aldol addition, the enolate of an aldehyde or a ketone reacts with the carbonyl carbon of a second molecule of aldehyde or ketone, forming a j8-hydroxyaldehyde or a jS-hydroxyketone. The new C—C bond forms between the a-carbon of one molecule and the carbon that formerly was the carbonyl carbon of the other molecule. The product of an aldol addition can be dehydrated to give an aldol condensation product. In a Claisen condensation, the enolate of an ester reacts with a second molecule of ester, eliminating an OR group to form a j8-keto ester. A Dieckmann condensation is an intramolecular Claisen condensation. A Robinson annulation is a ring-forming reaction in which a Michael reaction and an intramolecular aldol addition occur sequentially. 

B.ii. The Dieckmann Condensation. Just as there is an intramolecular version of the aldol condensation, there is an intramolecular version of the Claisen condensation but it has been given a different name, the Dieckmann condensation. 109,110 reaction involves intramolecular cyclization of an a, co-diester such as... 

Addition of enolate anions derived from aldehydes or ketones (aldol reactions) and esters (Claisen and Dieckmann condensations) to the carbonyl groups of other aldehydes, ketones, or esters. 

Ciaisen and Dieckmann Condensations Ciaisen and Aldol Condensations in the Bioiogicai Worid... 

Note that aldol, Claisen, and Dieckmann condensations all give primary products with oxygens in a 1,3 relationship. The Michael reaction with enolate anions gives products with oxygens in a 1,5 relationship. These relationships are a consequence of the polarization of the reagents. In aldol, Claisen, and Dieckmann condensations, the carbonyl carbon is positive and the a-position is negative. 

These types of EGBs promote many base-catalyzed reactions such as Dieckmann condensation [l],Wittig reaction[l], aldol condensation... 

We recall that intramolecular aldol condensation reactions can occur to give five- or six-membered ring compounds (Section 22.9). An intramolecular Claisen condensation, known as the Dieckmann condensation, can also occur to give five- or six-membered ring compounds. The Dieckmann condensation is more favorable than the bimolecular Claisen condensation because it converts a single molecule of reactant into two molecules of product. 

When the Claisen ester condensation is intramolecular, it goes by the name of the Dieckmann condensation. As with the intramolecular aldol reactions, only processes that give rise to five- or six-membered rings are favorable (Figure 17.33). This process has been used in the total synthesis of prostaglandin A2 (Figure 17.34). 

Intramolecular Claisen condensations can be carried out with diesters, just as intramolecular aldol condensations can be carried out with diketones (Section 23.6). Called the Dieckmann cyclization, the reaction works best on 1.6-diesters and 1,7-diesters. Intramolecular Claisen cyclization of a 1,6-diester gives a five-membered cyclic /3-keto ester, and cyclization of a 1,7-diester gives a six-membered cyclic /3-keto ester. 

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis Bucherer reaction Cannizzaro reaction Claisen aldol condensation Claisen condensation Claisen-Schmidt reaction. Clemmensen reduction Darzens glycidic ester condensation Diazoamino-aminoazo rearrangement Dieckmann reaction Diels-Alder reaction Doebner reaction Erlenmeyer azlactone synthesis Fischer indole synthesis. ... 

The use of classical condensation reactions is important. Thus, the Dieckmann reaction (equation 38) and the Thorpe-Ziegler cyclization (equation 39) have been used for almost a century for the preparation of a wide range of monocyclic and benzo-fused heterocycles. The aldol condensation and related reactions have also been fairly widely exploited, especially for the synthesis of 4-quinolones (the Camps reaction, e.g. equation 40), and various extensions of this general approach are described in the monograph chapters. 

Condensation reactions of the aldol type play an important part in heterocyclic chemistry. There are a large number of condensation reactions that are closely related to the aldol condensation. Each of these reactions has its own name Claisen, Dieckmann, Doebner, Knoevenagel, Perkin, to mention a few, but the chemistry is essentially the same as that of the aldol condensation. 

Condensations such as aldol (intermolecular, intramolecular), Claisen, and Dieckmann... 

---