Silyl ether, alcohol protecting group

A common OH protecting group is a silyl ether. A silyl ether has a new O-Si bond in place of the O-H bond of the alcohol. The most widely used silyl ether protecting group is the tert-butyldimethylsilyl ether. 

Silyl-derived protective groups are also used to mask the thiol function. A complete compilation is not given here since silyl derivatives are described in the section on alcohol protection. The formation and cleavage of silyl thioethers proceed analogously to simple alcohols. The Si—S bond is weaker than the Si—O bond, and therefore sulfur derivatives are more susceptible to hydrolysis. For the most part silyl ethers are rarely used to protect the thiol function because of their instability. Silyl ethers have been used for in situ protection of the — SH group during amide formation. ... 

The hydrosilylation of carbonyl compounds by EtjSiH catalysed by the copper NHC complexes 65 and 66-67 constitutes a convenient method for the direct synthesis of silyl-protected alcohols (silyl ethers). The catalysts can be generated in situ from the corresponding imidazolium salts, base and CuCl or [Cu(MeCN) ]X", respectively. The catalytic reactions usually occur at room tanperature in THE with very good conversions and exhibit good functional group tolerance. Complex 66, which is more active than 65, allows the reactions to be run under lower silane loadings and is preferred for the hydrosilylation of hindered ketones. The wide scope of application of the copper catalyst [dialkyl-, arylalkyl-ketones, aldehydes (even enoUsable) and esters] is evident from some examples compiled in Table 2.3 [51-53],... 

The ability to convert a protective group to another functional group directly without first performing a deprotection is a potentially valuable transformation. Silyl-protected alcohols have been converted directly to aldehydes, ketones, bro-mides, acetates, and ethers without first liberating the alcohol in a prior deprotection step. 

Silyl ethers are among the most frequently used protective groups for the alcohol function. This stems largely from the fact that their reactivity (both formation and cleavage) can be modulated by a suitable choice of substituents on the silicon atom. Both steric and electronic effects are the basic controlling elements that regulate the ease of cleavage in multiply functionalized substrates. In plan-... 

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

A variety of alcohols, protected as t-butyldimethylsilyl (TBDMS) ether derivatives, can be rapidly regenerated to the corresponding hydroxy compounds on alumina surface using MW irradiation (Scheme 6.8) [42], This approach prevents the use of corrosive fluoride ions that are normally employed for cleaving the silyl protecting groups. 

During the past 2 years several research groups have published research that either uses or expands upon Crowe s acyclic cross-metathesis chemistry. The first reported application of this chemistry was in the synthesis of frans-disubstitut-ed homoallylic alcohols [30]. Cross-metathesis of styrenes with homoallylic silyl ethers 15, prepared via asymmetric allylboration and subsequent alcohol protection, gave the desired trans cross-metathesis products in moderate to good yields (Eq. 15). 

The secondary hydroxyl group of 206 is now protected with a PMB group. Reduction of the resulting diastereomeric mixture 207 gives the corresponding alcohol 208, which is then separated to give a single stereoisomer. A silyl ether... 

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