Silyl protecting groups, for alcohols

Fully substituted alkenes are hydrosilylated with aluminum chloride without double-bond migration. The products have tertiary alkyl groups and thus may be utilized as silyl protecting groups for alcohols and related functional groups. " For example, chlorodimethylthexylsilane (49) is readily prepared from 2,3-dimethyl-2-butene (equation 42). 

Protection of Alcohols. Tribenzylchlorosilane is highly reactive towards nucleophilic displacement of chloride ion," but it has found only limited application as a bulky silyl protecting group for alcohols. The protection of the allylic alcohol (1) as the tribenzylsilyl ether (2) (eq 1) allowed for high 7r-facial selectivity in a subsequent epoxidation reaction at the 10,11-double bond. The trihenzylsilyl ether group can be efficiently depro-tected to the free alcohol using ACOH/THF/H2O (3 1 1) at room temperature. ... 

Silyl Ethers as Protective Groups for Alcohols. Oxidative Deprotection and Stability Under Alcohol Oxidation Conditions, Muzart. J. Synthesis. 1993, 11... 

Silyl protecting groups are the gold standard for the protection of alcohols.234 Novel photochemically removable protection groups for alcohols have been developed by Brook et a/.23S and Pirrung et al,236 For instance, cyclo-pentanol can be reacted with tris(trimethylsilyl)chlorosilane 53 in the presence of a mild base to yield the protected silyl ether 54. The protection group can be removed conveniently upon UV irradiation or by the use of Bu4NF (Scheme 12). 

We can also easily convert hydroxyl groups to silyl ethers. Section 14-10B covered the use of the triisopropylsilyl (TIPS) protecting group for alcohols. Similarly, sugars can be converted to their silyl ethers by treatment with a silyl chloride, such as chlorotrimethylsilane (TMSC1), and a tertiary amine, such as triethylamine. 

Q Additional coverage on silyl ethers addresses their use as protecting groups for alcohols and carbohydrates. 

Silyl ethers are versatile protecting groups for alcohols... 

Silicon-based protecting groups for alcohols are the best because they are the most versatile. They are removed by nucleophilic displacement with fluoride or oxygen nucleophiles and the rate of removal depends mostly on the steric bulk of the silyl group. The simplest is trimethylsilyl (Mt Si or often just TMS) which is also the most easily removed as it is the least hindered. Tn fact, it is removed so easily by water with a trace of base or acid that special handling is required to keep this labile group in place. 

In this section, the formation and cleavage of eight protecting groups for alcohols and phenols are presented acetate acetonides for diols benzyl ether para-methoxybenzyl (PMB) ether methyl ether methoxymethylene (MOM) ether ferf-butyldiphenylsilyl (TBDPS) silyl ether and tetrahydropyran (THP). 

Substituted silyl groups (R3Si-, where R is alkyl or aryl) are widely used as protecting groups for alcohols. A variety of reagents are available for this purpose, from simple and... 

Another type of protecting group for alcohols is a silyl ether. A silyl ether has the general formula of R —O—SiR3. The reaction of an alcohol with a trialkylsilyl halide leads to a trialkylsilyl ether in near-quantitative yield... 

Silyl ether (Section 13.6) A substance with the structure RaSi—O—R. The silyl ether acts as a protecting group for alcohols. 

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