Design of Tools for Organic Synthesis

In spite of the elegant solution to the problem as represented in the structure of 206, it is rather far from being optimal. In fact, the presence of the naphthalene system in this base made the latter rather vulnerable to electrophilic attack directed at aromatic rings. Owing to this complication, 206 is used in syntheses less often than other sterically hindered bases like 4-methyl-2,6-di-tcrt-butylpyridine 207, ethyldiisopropylamine, 208 (Hunig s base) or ethyldi-cyclohexylamine 209. All of these reagents are now manufactured commercially and widely used in cases where it is essential to carry out a reaction with strong electrophiles under strictly non-acidic conditions with the removal of proton acids as they are formed. In fact, the preparation of 205 was succesfully carried out in the presence of 208. ° 

The vast utilization of hindered secondary amines like diisopropylamine or dicyclohexylamine in carbanion chemistry is also based on the difference in their behavior toward protons and other electrophiles. Thus quite a number of the methods depend upon the use of the lithium or magnesium salts of these amines for the generation of carbanionic species. These salts are very strong kinetic bases and therefore are able to abstract a proton from a variety of C-H acids. At 

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