Alcohols triphenylsilyl

The 0-silylation reaction of alcohols is important as a protection method of hydroxyl groups. 0-Silylations of liquid or crystalline alcohols with liquid or crystalline silyl chlorides were found to be possible in the solid state. For example, when a mixture of powdered L-menthol (26), ferf-butyldimethylsilyl chloride (27), and imidazole (28) was kept at 60 °C for 5 h, 0-tert-butyldi-methylsilyl L-menthol (29) was obtained in 97% yield [8] (Scheme 4). Similar treatments of 26 with the liquid silyl chlorides, trimethyl- (30a) and triethylsilyl chloride (30b), gave the corresponding 0-silylation products 31a (89%) and 31b (89%), respectively, in the yields indicated [8] (Scheme 4). However, 0-silylation of triisopropyl- (30c) and triphenylsilyl chloride (30d) proceeded with difficultly even at 120 °C and gave 31c (57%) and 31d (70%), respectively, in relatively low yields. Nevertheless, when the solvent-free silylation reactions at 120 °C were carried out using two equivalents of 30c and 30d, 31c (77%) and 31d (99%) were obtained, respectively, in relatively high yields. 

Triphenylsilyl potassium adds like triphenylmethyl sodium to formaldehyde, giving the expected alcohol. 

Dienes.1 The titanium reagent 2, obtained from 1 by metallation and reaction with Ti(0-/-Pr)4, reacts with aldehydes to give (3-triphenylsilyl alcohols (3). These can be converted into either (E)- or (Z)-l,3-dienes by treatment with acid or base. 

Phenyl(triphenylsilyl)carbene has also been trapped without the interference of a silylcarbene-to-silene rearrangement84. It undergoes 0,H insertion with alcohols and is oxidized to the ketone by DMSO the latter reaction is likely to include an S-oxide ylide (equation 56). 

Triphenylphosphonio)ethyl carbonates, to protect alcohols, 107 2-(Triphenylphosphonio)isopropyl carbamates, to protect amines, 326, 342 Triphenylsilyl ethers, to protect alcohols,... 

In a synthesis of Epothilones A and B, Danishefsky and co-workers used a triphenylsilyl ether to protect a hindered secondary alcohol in a long sequence that included DDQ deprotection of a benzyl ether, dithiane hydrolysis, dimethyl acetal hydrolysis with p-toluenesulfonic acid in dioxane-H20 (5 1) at 50 °CT... 

The efficiency of kinetic resolution is even greater when there is a silicon or iodo substituent in the (3 )-position of the C-1 chiral allylic alcohols. The compatibility of silyl substituents with asymmetric epoxidation conditions was first shown by the conversion of (3 )-3-trimethylsilylallyl alcohol into (2/ ,3/ )-3-trimethylsilyloxiranemethanol in 60% yield with >95% and further exploited by the conversion of ( )-3-(triphenylsilyl)-2-[2,3- H2]propenol into (2 ,3/ )-3-triphenylsilyl[2,3- H2]oxirane-methanol in 96% yield and with 94% gg.io7b,i07c. pentyl group at C-1, the k,A for asymmetric... 

The key step of the synthesis is the rearrangement of the a-acetylenic alcohol 97 into the unsaturated carbonyl compound 124. This rearrangement was carried out with tris(triphenylsilyl)vanadate, triphenylsilanol and benzoic acid to give a mixture of the isomers 124 and 125. The latter was converted by iodine catalysis into the desired isomer 124. This key intermediate was afterwards transformed into the Cis-phosphonium salt 123 by standard procedures. The Wittig olefination of the Cio-dial 45 first with the fucoxanthin end group 123 and then with the peridinin end group 122 gave, in five steps, the C4o-carotenoid 126. Finally the epoxidation of this compound resulted in optically active fucoxanthin (121) and its (5S,6R)-isomer (Scheme 28). 

Triphenylsilyl ethers are typically prepared by the reaction of the alcohol with triphenylsilyl chloride (mp 92-94 °C) and imidazole in DMF at room temperature. The dehydrogenative silylation of alcohols can be accomplished with as little as 2 mol% of the commercial Lewis acid tris(pentaf1uorophenyl)borane and a silane such as triphenylsilane or triethylsilane [Scheme 4.98]. Primary, secondary, tertiary and phenolic hydroxyls participate whereas alkenes, alkynes, alkyl halides, nitro compounds, methyl and benzyl ethers, esters and lactones are inert under the conditions. The stability of ether functions depends on the substrate. Thus, tetrahydrofurans appear to be inert whereas epoxides undergo ring cleavage. 1,2- and 1,3-Diols can also be converted to their silylene counterparts as illustrated by the conversion 983 98.4. Hindered silanes such as tri-... 

General Considerations. Like other bulky trialkylsilyl groups, the triphenylsilyl group was introduced to serve as a hydrolytically stable protecting group for alcohols. The hydroxyl functionality can be easily derivatized using Ph3SiCl in the presence of a tertiary amine or imidazole as a base (eqs 1 and 2). ... 

Protecting Group. Triphenylsilane is used in certain cases for the preparation of triphenylsilyl ethers, which serve as alcohol protecting groups. The triphenylsilyl group is considerably more stable (about 400 times) than the TMS group toward acidic hydrolysis. ... 

The combination of tris(triphenylsilyl) vanadate and triphenylsilanol has been found to promote the conversion of a-acetylenic alcohols to aj8-unsaturated carbonyl compounds with high efficiency. ... 

The excellent enantioselectivities generally achieved with titanium tartrate-catalyzed epoxidation of allylic alcohols with ferf-butylhydroperoxide was exploited, for example, for the preparation of (2S,3S)- and (2/ ,3f )-[2,3- H2]oxiranes (72), two valuable chiral building blocks (Figure 11.28). By using a slightly modified Sharpless procedure, ( )-3-triphenylsilyl-2-[2,3- H2]propenol (20) was converted into the (S,S)- and (/ ,/ )-forms, respectively, of 3-triphenylsilyl[2,3- H2]glycidol (71). The hydroxylmethyl substituent... 

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