Synthetically important organic

This volume is a companion to Part B, Reactions and Synthesis. Part B emphasizes the synthetically important organic reactions. It adds some further mechanistic information, but is aimed primarily at introducing to students the available repertoire of organic reactions and providing an opportunity to develop a background in synthetic methodology. 

The synthetic importance of the malonic ester synthesis follows from the fact that the substituted malonic ester can easily be hydrolyzed, and subsequently decarboxylates to yield a substituted acetic acid 9. This route to substituted acetic acids is an important method in organic synthesis ... 

In general however, ozonolysis is of limited synthetic importance. For quite some time ozonolysis has been an important tool for structure elucidation in organic chemistry, but has lost its importance when spectroscopic methods were fully developed for that purpose. The identification of the aldehydes and/or ketones obtained by ozonolysis of unsaturated compounds allowed for conclusions about the structure of the starting material, but has practically lost its importance since then. 

Nitrilases catalyze the synthetically important hydrolysis of nitriles with formation of the corresponding carboxylic acids [4]. Scientists at Diversa expanded the collection of nitrilases by metagenome panning [56]. Nevertheless, in numerous cases the usual limitations of enzyme catalysis become visible, including poor or only moderate enantioselectivity, limited activity (substrate acceptance), and/or product inhibition. Diversa also reported the first example of the directed evolution of an enantioselective nitrilase [20]. An additional limitation had to be overcome, which is sometimes ignored, when enzymes are used as catalysts in synthetic organic chemistry product inhibition and/or decreased enantioselectivity at high substrate concentrations [20]. 

The replacement of a halide or sulfonate by cyanide ion, extending the carbon chain by one atom and providing an entry to carboxylic acid derivatives, has been a reaction of synthetic importance since the early days of organic chemistry. The classical conditions for preparing nitriles involve heating a halide with a cyanide salt... 

He never gave unbridled rein to his synthetic efforts, nor did he fall into the temptation of purposeless synthesis. He always remained a true scientist—a student of nature.. . . This great individual was a man of inflexible veracity and simplicity.. . . Emil Fischer s life was based on responsibility a responsibilityfor the austerity andpurity of his work and its aims, responsibility for the university as an important organ of our cultural and economic life, and responsibility for each of his students. 

The Michael additions to 1 - 3 of a large variety of carbon, nitrogen, oxygen, sulfur and selenium nucleophiles, as well as hydride, followed by inter- or intramolecular transformations of the chlorine substituent or/and the methoxy-carbonyl fragment, offer versatile synthetic approaches to a large variety of synthetically useful and important organic molecules. 

An additional modification in the above synthetic scheme is possible by introducing the aromatic diamine in the form of its trimethylsilyl derivative [72]. Monotrimethylsilyl-substituted amines are readily prepared from the free amine with hexamethyldisilazane or trimethylsilyl chloride in the presence of a tertiary amine [73, 74] whereas bis(trimethylsilyl)-substituted amines require more aggressive reagents, such as butyllithium in conjunction with trimethylsilyl chloride [75]. As illustrated in Scheme 19, monotrimethylsilyl-substituted amines react with acyl chlorides to form the corresponding amides and liberate trimethylsilyl chloride. Monotrimethylsilyl-substituted amines are reported to display increased reactivity with acyl chlorides [76], This is of great synthetic importance since the increased reactivity allows for reaction with low basicity amines. Bis(trimethylsilyl)-substituted amines, on the other hand, react with acyl chlorides to form the corresponding JV-trimethylsilyl amides, see Scheme 20. The JV-trimethylsilyl amides are much more soluble in common organic solvents. However, they are hydrolytically unstable and readily convert back to the free amides. 

---