Protec tion/deprotection

Water-soluble compounds could be used in their native form without the need for hydrophobic derivatisation, again eliminating tedious protec-tion deprotection steps from the synthetic route. 

Figure 6.100 Synthesis of isotopically labeled monoalkylated malonates following a protec-tion/deprotection approach...

When the aikene is nonsymmetric, the addition reaction is exclusively Markovnikov and generally nonstereospecific. Some examples are shown in Figure 11.11. The first two examples proceed through a tertiary carbocation. In the third example, we see that alcohols can be added in the same way as water. The last reaction of this group is widely used as the first step of a protec-tion/deprotection sequence for alcohols we will meet this again later, when we look more closely at synthesis. Notice the role of the lone pair on oxygen stabilizing the adjacent carbocation. 

Strat- egy N -Protec- tion N -Deprotection Side-Chain Protection Final Deprotection Mode of Synthesis Ref... 

For instance, 89 was converted into 90 in 96 % yield, which could be transformed into 91-93 by nucleophilic additions to the C=N-bond. The nitrile function of 92 can be hydrolyzed to the amino acid, and the olefmic moiety in 91-93 may be submitted to a manifold of addition reactions (Fig. 34). After N-protec-tion and 0-deprotection prolinols 91-93 can be oxidized to prolines. 

Deprotection of the amino groups followed by cyclization and Fmoc-protec-tion of the exocyclic amino group dehvers the desired BAZ derivative 114, and quite analogously, 115 (Fig. 42). 

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