1.    Removal of Silyl Groups from Protected Phenols
            Silyl-protecting groups are known to be easier to remove from phenolic oxygen atoms than
        from silyl protected aliphatic oxygen atoms. Classic methods for performing such reactions include
        non-acific fluoride sources such as tetrabutylammonium fluoride, potassium fluoride/alumina and
        KF in the presence of an appropriate crown ether.
                We developed a two-phase system using powdered NaOH and a phase transfer catalyst,
        tetrabutylammonium hydrogen sulfate, in dioxane. This method allows the removal of silyl groups
        from protected phenols without deprotecting silyl-protected alcohols.

        For details, see: Tetrahedron Letter 1999, 40, 3133 - 3136

2.    Selective Deprotection using ZnBr₂ and H₂O in CH₂Cl₂
                Several years ago, we learned that ZnCl₂ in the presence of a small amount of water could cause
        the cleavage of some silyl ethers. But, results tended to be uneven. More recently, an article describing
        ZnBr₂-mediate reactions in which ZnBr₂ served as a Lewis acid prompted us to attempr desilylation
        reactions using this mild acid. Our work showed that large silyl groups are less susceptible to hydrolysis
        than smaller groups and allows for the selective removal reactions shown below.

                           
                          
 
        For details, see: Tetrahedron Letter 2002, 43, 7151` - 7153