Benzylidene acetals amine protection

The simultaneous protection of the 3 and S hydroxy groups of nucleosides and the 4,6- or 3,4-hydroxyls of hexopyranoses is a common problem in organic synthesis. In the case of hexopyranoses, we have already seen that benzylidene acetals and, in certain circumstances, isopropyiidene acetals can be used to good effect. An alternative silicon-based group would offer a wider repertoire of conditions for mild deprotection and such a group was devised by Markiewicz the 1,1,3,3-tetraisopropyldisiloxanylidene group (abbreviated TIPDS),22 229 TIPDS groups are stable to water, 0.3 M p-toluenesulfonic acid in dioxane, 10% tri-fluo mace tic acid in chloroform, 5 M ammonium hydroxide in dioxane-H20 (4 1), and tertiary amines in pyridine,... 

In one additional example, illustrating the applicability of the Ferrier cyclization to amine-based substrates, the same strategy allowed the synthesis of carba-glucosamine (Scheme 8.33). Starting from Cbz protected methyl a-D-glucosaminide 123, 4,6-benzylidene formation, di-benzylation, cleavage of the acetal, regioselective iodination and simultaneous elimination... 

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