Cleavage of silyl ether

Tetrabutylammonium fluoride (TBAF) is usually used in the form of the trihydrate or as a solution in tetrahydrofuran (THF). The pure form is difficult to isolate, owing to decomposition to FFF, tributylamine, and but-l-ene [18, 19] on dehydration. It has been used for a variety of reactions, including as a catalyst for various reactions with silicon compounds [20, 21]. One of its main uses is in the cleavage of silyl ether protecting groups [22]. 

A new section covers the formation and cleavage of silyl ethers, and their strategy and use as protecting groups on alcohols. This new material introduces the concept of... 

Tris(pentafluorophenyl)borane [B(CgFj)3], is a powerful and selective Lewis acid catalyst used in many reactions in organic chemistry [1 ]. Parks and Piers [5] found that B(CgFj)3 catalyzes the hydrosilylation of carbonyl compounds. The silylation of alcohols with the formation of Ft as the only by-product [6] and the cleavage of silyl ether and ether bonds catalyzed by B(C F5)3 [7, 8] provide an... 

Table 1 Half-lives in the cleavage of silyl ethers...

The weakly electrophilic properties of iodine make it a mild Lewis acid with potential for selective cleavage of silyl ethers as shown in Scheme 4,42.M... 

Cleavage of silyl ethers. Fetra-n-butylammonium fluoride is a powerful agent for cleavage of silyl ethers. It is particularly useful for cleavage of the recently introduced dimethyl-/-butylsilyl ethers (see Dimethyl-r-butylchlorosilane, this volume). The ethers are cleaved rapidly to alcohols by treatment with 2-3 eq. of the fluoride in THF at... 

Fluoride ions are applicable deprotecting reagents for the cleavage of silyl ethers. Several fluoride sources are available The widely used tetrabutylammonium fluoride (TBAF), which is a basic agent and can cause several undesired side reactions, the acidic HF acetonitrile complex and the HF-pyridine complex. In this case only the benzylic TBS ether is cleaved, because the reaction is carried out at room temperature. ... 

Numerous methods are now available in the literature for the deprotection of TBS ethers under a variety of conditions. One of the most effective ways for the cleavage of silyl ethers is based on the exploitation of the high affinity of silicon towards fluoride ions. Thus, a number of reagents involving one form of fluoride or another, such as tetrabutylammonium fluoride [292], BF3-Et20 [301], hydrofluoric acid [302], fluorosilicic acid [303], ammonium fluoride [304], silicon fluoride [305], lithium tetrafluoroborate [306], and chlorotrimethylsilane/potassium fluoride dehydrate [307] have been developed for the deprotection of TBDMS ethers. Among these, TBAF is most frequently used but the strong basicity of the fluoride anion makes it inappropriate for base sensitive functionalities. 

Typical procedure for cleavage of silyl-ether (Scheme 41) [269] Under an Ar atmosphere the resin was slurried in THF (7 mL) and HF-pyridine (Aldrich,... 

Fig. 40. Chemiluminescent decomposition of adamantyl aromatic dioxetanes by fluoride-induced cleavage of silyl ether side chains. The 2,6-substitution pattern shown in (a) has a quantum efficiency of 0.01%, whereas the 2,4-substitution pattern shown in (b) has a quantum efficiency of 45%. The data [which are taken from the work of Schaap et al. (S8)] can be rationalized by considering the mechanism suggested in Fig. 39.

Hydrolysis. Hydrolytic cleavage of silyl ethers under PTC conditions shows selectivity. Phenolic TBS ethers are preferentially removed. ... 

Selective cleavage of silyl ethers. - T CH2CI2 or CH3CN at 25" in rates that are The relative rates are in the order Et-.Si 5 phenols are stable to Sip4 in CH CI at 23 selective cleavage of primary or secondary... 

Silyl Ethers. - The selective cleavage of silyl ethers has been achieved using silicon tetrafluoride in dichloromethane or acetoniuile, and the use of methanol as solvent for the tetra-n-butylammonium fluoride- mediated desilylation of silyl ethers in the presence of base-sensitive groups has been described. ... 

Silvl Ethers.- The reductive cleavage of silyl ethers employing NaH in HMPA or DMPU has been reported. Methyl 6-Q-tert-butyldimethylsilyl-a-D-glucopyranoside and the 4,6-di-Q-tert-butyldimethylsilyl ether of D-glucal were each deprotected in 90% yield under these conditions. The deprotonation of a silyl ether with base is mentioned in Chapter 13. The trimethylsilyl ethers of a number of D-glucose derivatives have been prepared and characterized by H-, c- and Si-n.m.r. spectroscopy and mass spectroscopy. 

Cleavage of silyl ethers with H2/Pd JACS (1972) 9 6190 footnote 4... 

SCHEME 13 Oxidative cleavage of silyl ether 30 to provide synthetic chinensiolide B (1). 

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