Nucleophile/base-labile protecting groups

This chapter examines nucleophile/base-labile protecting groups. The majority of the functional groups described in this book are based on heteroatoms that, by virtue of higher electronegativity or more diffuse orbitals, can support a negative charge more effectively than carbon. Consequently, some protecting groups can be cleaved by expulsion of the functional group as an anion either by elimination or by nucleophilic substitution. Whether or not activation is necessary depends upon the leaving group ability of the protected functional group, the nucleophilicity of the attacking species, the solvent, and the steric availability at the electrophilic site. The chapter then looks at protecting group cleavage by SN2 chemistry and by nucleophilic addition, as well as deprotection by β-elimination. It also considers allylic protecting groups.