Ethers, r-butyldimethylsilyl

Rexyn 101 (polystyrene sulfonic acid), 80-91% yield.This method does not cleave the r-butyldimethylsilyl ether. 

DMSO, H2O, dioxane, reflux, 12 h, 65-99% yield.These conditions cleave a dimethyl ketal in the presence of a r-butyldimethylsilyl ether. 

Bu4N F, THF, 0°, 1 h, 52-95% yield.A primary alcohol protected as the r-butyldimethylsilyl ether is cleaved under these conditions, but a similarly protected secondary alcohol is stable. 

Reduction of a-methyl-fi-hydroxy ketones,2 The r-butyldimethylsilyl ethers of these ketones, in which chelation is difficult, are reduced by lithium aluminum hydride with a high degree of 1,2-anri-selectivity. This reaction can therefore afford either aM ,a/iri-l,3-diols or anti,syn- 1,3-diols with high selectivity. 

Detritylation Trityl ethers are cleaved by reaction with formic acid in ether in high yield in 7-45 minutes. Under these conditions isopropylidene and benzyl-idene acetals and r-butyldimethylsilyl ethers are not affected, but tetrahydropyranyl ethers are partially cleaved. 

Cyclization of a variety of y-allenic alcohols with silver nitrate proceeds by 5-exo cyclization to form 2-alkenyltetrahydrofurans (equation 87).205c 206 Little stereoselectivity is seen in cyclizations of secondary alcohols. Cyclization by intramolecular oxypalladation/methoxycarbonylation or oxymercuration followed by transmetallation and methoxycarbonylation also showed no stereoselectivity (equation 88 and Table 24, entries 1 and 2).50 207 However, cyclization of the corresponding r-butyldimethylsilyl ether derivatives with mercury(II) trifluoroacetate followed by transmetallation/methoxycarbonylation pro-... 

The mixture of chromium trioxide with one equivalent of trimethylsilyl chloride, with no solvent added, results in the formation of an explosive red liquid that is soluble in dichloromethane or tetrachloromethane.428 It is suggested, with no spectroscopic evidence, that it consists of trimethylsilyl chlorochromate [Me3Si-0-Cr(0)2-Cl]. This compound, which can safely be used in organic solvents, is able to oxidize alcohols to aldehydes or ketones, and interacts with r-butyldimethylsilyl ethers producing deprotection, followed by oxidation of the liberated alcohol.138 Compounds analogue to trimethylsilyl chlorochromate are also able to oxidize alcohols, although they possess lesser reactivity. They can be prepared by reaction of chromium trioxide with dimethyldichlorosilane and diphenyldichlorosilane.428b... 

This triflate has been prepared by reaction of r-butyldimethylsilyl chloride with silver triflate (expensive)1 or triflic acid (80% yield).2 Since this triflate is sensitive to moisture, it should be used soon after preparation. In combination with 2,6-lutidine, it converts even tertiary alcohols into r-butyldimethylsilyl ethers in 70-90% yield. 

Trimethylsilyl ethers.2 These protective derivatives of alcohols are conveniently prepared with K2COj or Na2C03 as base and Aliquat 336 as the phase-transfer catalyst (65 95% yield). r-Butyldimethylsilyl ethers can be prepared in the same way. 

Selective cleavage of t-butyldimethylsilyl ethers. This reagent cleaves r-butyldimethylsilyl ethers at 22-55° in 80-92% yield in the presence of r-butyl-diphenylsilyl ethers. 

Cleavage of MOM ethers. Methoxymethyl ethers are cleaved by this reagent at 0° in 80-97% yield. Acetals and THP, trityl, and r-butyldimethylsilyl ethers also are cleaved, but less readily.-... 

Selective oxidation of secondary alcohols.1 This oxidant is almost as effective as PCC, but is less acidic and does not attack r-butyldimethylsilyl ethers. This property allows selective oxidation of a secondary hydroxyl group in the presence of the silyl ether of a primary hydroxyl group. 

PDC with tiimethylsilyl chloride s is not only a rapid oxidizing agent for alcohols, but will also effect a deprotection-oxidiation sequence for silyl ethers. Both trimethylsilyl and r-butyldimethylsilyl ethers, which are normally stable to PDC, can be transformed directly into the corresponding carbonyl compounds in good yield (Table 13). 

The TBS ether protecting group is more stable to hydrolysis than the trimethyl-silyl ether by a factor of 10" but is still readily cleaved by exposure to either n-Bu4NF in THF, HF-pyridine, CsF in DMF, or H2SiFg. Diisobutylaluminum hydride is another reagent for the deprotection of r-butyldimethylsilyl ethers under mild conditions. 

Allylic alcohols from epoxides. Reaction of 1 with epoxides and then DBN gives reasonable yields of allylic alcohols as the r-butyldimethylsilyl ether. 

Further work on the catalytic efficacy of (108) has shown that the compound is an efficient promoter for the reduction of aldehydes (92-96% yields) and most ketones (64—95% yields) by poly(methylhydrosiloxane) and also an efficient catalyst for the desilylation of r-butyldimethylsilyl ethers (68-94% yields). ... 

SEM ethers are stable to the acidic conditions (AcOH, H2O, THE, 45°C, 7h) that are used to cleave tetrahydropyranyl and r-butyldimethylsilyl ethers. Overall, this is a very robust protective group that is often difficult to remove. ... 

Although alkylation of 3-hydFoxy ester dianions occurs with high diastereofacial selectivity, the aldol reaction of the dianion obtained from methyl 3-hydroxybutanoate with benzaldehyde gives all four dia-stereomeric aldols in a ratio of 43 34 14 9 (equation 117). On the other hand, dianions of 8-hydroxy esters show rather good diastereofacial preferences under the proper conditions. Deprotonation of t-butyl-5-hydroxyhexanoate with lithium diethylamide in the presence of lithium triflate gives an enolate that reacts with benzaldehyde to give aldols (196) and (197) in a ratio of 91 9 (equation 118). Use of the r-butyldimethylsilyl ether instead of the alcohol resulted in no facial preference. 

Diastereomeric mixtures of vicinal nitro alcohols obtained by a classical Henry reaction with low dia-stereoselectivity can be easily silylated to give the corresponding mixture of O-r-butyldimethylsilyl ethers.26 The latter undergoes an enrichment of the erythro isomer (54 up to >95 5) by treatment with LDA and successive protonation of the corresponding lithium salts (Scheme 8), which occurs with high diastereoselectivity. 

Cleavage of TBS ethers. Many other protecting groups are not affected when r-butyldimethylsilyl ethers are cleaved with IBr in MeOH. 

Cleavage of THP-ethers. The boron trifluoride etherate-ethanethiol mixture cleaves THP ethers at low temperatures without affecting the methylenedioxy group, acetonides, mesitaldehyde acetals, methoxymethyl ethers, and r-butyldimethylsilyl ethers. 

Reductive cleavage of t-butyldimethylsilyl ethers. r-Butyldimethylsilyl ethers are generally cleaved by fluoride ion, but they can also be reductively cleaved by DIBAH in CH2CI2 at 23 in 1-2 hours to yield the corresponding alcohols in 84-91% yield. 

Desilylation. This acid is less acidic ih jffect on acid-labile protecting groups. A funhi f r-butyldimethylsilyl ethers in the presence hers. The selectivity of H2S1F6 can be enh -ffective than DMAP). The cleavage is effecu jfter one hour. 

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