Triphenylsilyl ethers

Reduction of ketones to triphenylsilyl ethers is effected by the unique Lewis acid perfluorotriphenylborane. Mechanistic and kinetic studies have provided considerable insight into the mechanism of this reaction.186 The salient conclusion is that the hydride is delivered from a borohydride ion, not directly from the silane. Although the borane forms a Lewis acid-base complex with the ketone, its key function is in delivery of the hydride. 

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

Triphenylsilyl ethers are similar in lability to TMS ethers toward basic hydrolysis but they are about 400 times more stable than TMS ethers towards acid hydrolysis. A triphenylsilyl ether group played an important strategic role in the finale of a synthesis of the polyether antibiotic Lonomycin A [Scheme 4.96],154 Model studies of the directed aldol reaction by which the lithium enolate 96.1... 

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... 

In the case of 0-silyl ethers, thermolysis of (triphenylsilyloxy)tetraphenylantimony (13) did not afford the ligand coupling product, phenyl(triphenylsilyl)ether. Instead, a disproportionation reaction took place to give the bis(silyloxy) ether (14) and pentaphenylantimony (3), which decomposed into triphenylantimony (4) and biphenyl (5) under the conditions of the reaction. 1... 

Triphenylsilyl ether aluminium acetylacetonate and triphenylarsonium-p-nitrophenacylide have been found to induce the photopolymerisation of acrylic monomers by a free radical mechanism while arylthiyl radicals induce the photopolymerisation of vinyl monomers (CH2=CHX) in the order X= -C(CH3)3 < -( 2)3 3 < -(CH2)Si(OCH3)3 <= -CH2Si(CH3)3 -Si(OCH3)3 -Si(CH3)3 ... 

Retinoids. Several routes have been described for the preparation of retinal and its derivatives. Two papers ° on the use of trimethylsilyl and triphenylsilyl protecting groups describe the preparation of the Ce intermediate -3-methyl-pent-2-en-4-yn-l-ol triphenylsilyl ether (100), and the four- or five-step synthesis of IIZ-retinal from this and the C14 aldehyde (101). A method for base-catalysed trans elimination of PhSOaH from the sulphone (102) affords retinyl acetate (103) in 86% yield. 

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-... 

An aluminum eontaining photoinitiation eatalyst was reported by Hayase and eoworkers It eonsists of the aluminum compound and o-nitrobenzyl triphenylsilyl ether. The o-nitrobenzyl triphenylsilyl ether photo decomposes to form triphenylsilanol ... 

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. ... 

Intermolecular a-alkylation of aldehydes with 2-(bromomethyl)acrylates 18 were developed by the Palomo group [8]. The reaction was best catalyzed by diphenyl-prolinol TMS (6 )(Scheme 25.5) or dihexylprolinol triphenylsilyl ethers (Scheme 25.6), and required the presence of an acid scavenger, such as DABCO or DMAP. 

Miscellaneous Reactions. o-Nitrobenzyl triphenylsilyl ether, a latent photogenerated source of triphenylsilanol, has been synthesized from o-NBA (eq 13). This new catalyst, upon irradiation at 365 nm, serves as a coinitiator in the polymerization of epoxides. ... 

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