Benzyl esters amine protection

Cbz-protected amines behave like amides—they are no longer nucleophilic, because the nitrogen s lone pair is tied up in conjugation with the carbonyl group. They are resistant to both aqueous acid and aqueous base, but they have, to use the analogy we developed in the last chapter, an Achilles heel or safety catch—the benzyl ester. The same conditions that removed benzyl ethers in Chapter 24 will remove Cbz HBr or hydrogenolysis. cleavage of Cbz (Z) in HBr/AcOH... 

AUcyl esters (e.g., methyl, ethyl, benzyl esters) are usually stable toward amines and, thus, are used as protecting groups. Some anecdotic examples of amide bond formation with aUcyl esters, however, are reported in the literature. High reaction temperature, addition of a Lewis acid (52), or use of organoaluminium species generated from DIBAL-H-H2NR (53) can enable these reactions. Saturated ammonia in methanol can also react with... 

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