Analysis Knoevenagel reaction

The preparation of (83) (Expt 8.29) is an example of the Hantzsch pyridine synthesis. This is a widely used general procedure since considerable structural variation in the aldehydic compound (aliphatic or aromatic) and in the 1,3-dicarbonyl component (fi-keto ester or /J-diketone) is possible, leading to the synthesis of a great range of pyridine derivatives. The precise mechanistic sequence of ring formation may depend on the reaction conditions employed. Thus if, as implied in the retrosynthetic analysis above, ethyl acetoacetate and the aldehyde are first allowed to react in the presence of a base catalyst (as in Expt 8.29), a bis-keto ester [e.g. (88)] is formed by successive Knoevenagel and Michael reactions (Section 5.11.6, p. 681). Cyclisation of this 1,5-dione with ammonia then gives the dihydropyridine derivative. Under different reaction conditions condensation between an aminocrotonic ester and an alkylidene acetoacetate may be involved. 

The catalytic performance of the NCNT was tested via the Knoevenagel condensation of benzaldehyde (BA) with ethylcyanoacetate (ECA) to form ethyl-a-cyanocinnamate (ECC). The NCNT (1 g) were crushed, heated to 423 K under vacuum and maintained under these conditions for 1 h. The reactants, BA (0.01 mol) and ECA (0.01 mol), were dissolved in ethanol (50 mL) and carbondioxide was removed using the freeze-thaw method. The solution was then added to the NCNT and the reaction was performed under reflux conditions. To monitor the progress of the reaction, samples of the reaction mixture were taken regularly for GC analysis. 

Samples of tridimensional microporous zinc phosphates with fully connected framework with structures type FAU and CZP have been prepared. The influence of some synthesis parameters on the nature of the crystalline phases obtained, such as crystallization time and temperature, concentration of the different reactives or pH, are discussed. Physicochemical characterization of the pure samples has been performed by different techniques ICP, XRD, C and P MAS-NMR, TG, TG-MS, in-situ thermal XRD analysis and SEM. These materials were tested in the Knoevenagel condensation of different esters and benzaldehyde. They have demonstrated a good selectivity and a higher activity than the basic zeolites previously described in the literature with these reactions. 

Retrosynthetic analysis of the target coumarin skeleton provides two major synthetic routes (Figure 10.1). Route A requires an aromatic o-hydroxy carbonyl compound and a two-carbon fragment observed in Knoevenagel and Perkin reactions reflecting the [4h-2] approach for the construction of six-membered heterocycles. Route B represents the reaction between phenols and three carbon fragments associated with the Pechmann cyclization. In recent years, newer synthetic methodologies have also been applied to the synthesis of a variety of coumarins that have avoided the use of concentrated sulfuric acid. The present chapter reviews various... 

The cyclization of 2 was carried out in deuterated solvent and base. When the reaction was performed with rigorous exclusion of air, the expected Knoevenagel product, deuterated in nine positions i-dg) could be detected by mass spectrome-tric analysis of the crude reaction mixture. Furthermore, octadeuterated tricyclic alcohol (5-reaction product after the reaction mixture was exposed to air (Scheme 1.4). ... 

The starting point in the investigation of a reaction mechanism is always the analysis of the number of products obtained in the reaction and the determination of their structures. Particularly, from the study of the structure of the reaction products we can obtain valuable information about the bonds that have been broken and those that have been formed during the process. In this case, the analysis of the structure of the reaction products 4 and 5 is the key to understanding why an ideal substrate for a Knoevenagel condensation as P-keto ester 2 reacts in a different way. 

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