Silyl and Germyl Linker Units

The use of silyl ethers as protecting groups for the hydroxyl functionality is well known, and their adaption into linker units was a welcome addition to the SPOS literature. Thus, many silyl linker units have been reported for alcohols, and a selection is illustrated in Table 1.15. Owing to the large number of reported examples, a complete discussion of each is beyond the scope of this chapter, but Spivey has written a complete review. Much like deprotection of their solution-phase counterparts, cleavage from silyl linkers can be achieved using, for example, HE (Table 1.15, Entries 1-3 and 6) , TBAF (Table 1.15, Entries AcOH (Table 1.15, Entries 1 and 4) °, or TEA (Table 1.15,Entry 5). Beyond alcohols, other traditional sUyl linker units are useful for SPOS with other substrates such as amines (Table 1.15, Entry 

By varying the electrophile, this class of linker can also be utilized in a multifunctional approach. In its simplest form, this has involved halogenation. For example, cleavage strategies for leaving bromine (Table 1.16, Entry 3)2 2,283 (Table 1.16, 

Entries 3 and 5)2 2-284 jjg cleavage site have been reported. Similar results 

Beyond simple halogenation of aromatics, other substrates supported through silyl linker units can be cleaved in a diversity fashion. For example, allylsilanes can be combined 

Finally, silicon-nitrogen bonds are also labile in the presence of electrophiles, and this concept has been used by Komatsu in development of a silylimine linker (Table 1.16, Entries 12-14). Multifunctional cleavage was achieved with a range of electrophiles. For example, treatment with TFA left a hydrogen residual at the point of attachment (Table 1.16, Entry 12), while benzoyl (Table 1.16, Entry 13) and allyl (Table 1.16, Entry 14) groups were introduced by cleavage with benzoyl chloride and allyl iodide, respectively. 

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