Claisen condensation internal

It Is of Interest to note that the preparation of dimethyldihydroresorcinol (also named dimed one and methone Section VII, 15) involves an initial IVIichael addition to mesityl oxide, followed by an internal Claisen condensation. 

An internal Claisen condensation of a diester forms a ring. Such an internal Claisen cyclization is called a Dieckmann condensation or a Dieckmann cyclization. Five- and six-membered rings are easily formed by Dieckmann condensations. Rings smaller than five carbons or larger than six carbons are rarely formed by this method. 

The low-energy tandem mass spectra of the deprotonated molecular ions of acylglycerol contain a type of ion whose formal mass-based composition corresponds to a ketone obtained by the combination of two fatty acid chains with a carbonyl group, minus a proton. The ketone contains mainly the chains of the central fatty acid combined with one of the two external fatty acids, even if the ketone containing the two external fatty acids is present with a much weaker intensity. The formation of these ions may be explained by an internal Claisen condensation followed by a fragmentation induced by a nucleophile substitution and then by a decarboxylation, as shown in Figure 8.64. 

Considerable attention was paid to the MS-MS characterization of TAG [2]. In an excellent study, Stroobant et al. [21] investigated the fragmentation of [M-H] of TAG, generated by desorption chemical ionization. A reversible rearrangement due to an internal Claisen condensation is proposed to explain the lower abundance of the DAG fragment resulting from the loss of the sn-2 fatly acid. Hsu and Turk [22]... 

Dieckmann cyclization internal Claisen condensation (Section 23.10)... 

The compound (III) can however lose ethanol by an internal Claisen ester condensation (p. 264) to give the cyclohexane derivative (IV), which, being the ester of a (3-keto acid, in turn readily undergoes hydrolysis and decarboxylation to give 5,5Hiimethyl cyclohexan-i,3Hiione (V) or Dimedone, a valuable reagent for the detection and estimation of formaldehyde. 

A 1-1. Claisen flask fitted with a dropping funnel and a thermometer dipping into the liquid is attached to a condenser set for downward distillation. In the flask are placed 150 g. of anhydrous sodium sulfate, 200 g. (108 cc.) of concentrated sulfuric acid, and 100 cc. of water. The flask is heated over a wire gauze, and while the internal temperature is maintained at 130-135°, the diazo-nium solution, in 25-cc. portions, is added at the same rate as the distillate is collected (Note 2). When this operation has... 

Esters of dicarboxylic acids having hydrogen on the 8 or e carbon atoms undergo intramolecular cyclisation when heated with sodium or with sodium ethoxide. This cyclisation is known as the Dieckmann reaction. It is essentially an application of the Claisen (or acetoacetic ester) condensation to the formation of a ring system the condensation occurs internally to produce a... 

Frequently the basic conditions used cause the initial Michael adduct to undergo intramolecular transformations, as for example in the synthesis of dimedone (Expt 7.11). This involves a Michael reaction between mesityl oxide and diethyl malonate followed by an internal Claisen ester condensation. 

The ester (III) may, however, get rid of one mole of ethanol by means of an internal Claisen-ester condensation to form the respective cyclohexane derivative (IV). 

A vacuum distillation apparatus using the components of the traditional organic laboratory kit is shown in Figure 16.5. It uses the ebulliator tube, the Claisen head, and a thermometer for internal temperature monitoring. A water condenser is shown, but with high-boiling liquids, this apparatus may be simplified by removing the water condenser. A special vacuum adapter allows connection to the manometer and vacuum source. 

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