1.3- diol monosilyl ethers

Thus, only few reports were disclosed for the [1,3] Brook isomerization Utimoto, Oshima and coworkers have reported that the treatment of tert-butyldimethyl(dibromomethyl)silane 64 with LDA followed by the addition of an excess of benzaldehyde lead to the 1,3-diol monosilyl ether 66 via the intermediacy of lithium carbenoid 65 (equation 24) . The rate of isomerization was dependent on the solvent used and HMPA was found to be the best solvent. ... 

The successive reaction of (dibromomethyl)silanes with LDA (hthium diisopropyl-amide) and two equivalents of benzaldehyde gives 1,3-diol monosilyl ethers in good yield (Scheme 10.221) [574]. This tandem reaction would proceed via anionic 1,3-silyl migration of /l-lithioxyalkylsilane intermediate 152 and addition of the resulting lithium carbenoid to benzaldehyde. Thus, internal activation of the silicon-lithium alkoxide promotes nucleophilic addition of a-haloalkylsilanes. Similar tandem reactions of 2-trimethylsilyl-l,3-dithiane with aldehydes [575] and epoxides [576] have been reported. 

Derivatives of 1,3- and 1,4-diols are stable to pH 4-10 at 22° for several hours, but derivatives of 1,2-diols undergo rapid hydrolysis under basic conditions (5 1 THF-pH 10 buffer, 22°, 5 min) to form monosilyl ethers of the parent diol. 

Recently, Schaumann et al. 153,154 an(j Bienz et tf/.155,156 have developed dependable routes for the resolution of racemic functionalized organosilanes with Si-centered chirality using chiral auxiliaries, such as binaphthol (BINOL), 2-aminobutanol, and phenylethane-l,2-diol (Scheme 2). For instance, the successive reaction of BINOL with butyllithium and the chiral triorganochlorosilanes RPhMeSiCl (R = /-Pr, -Bu, /-Bu) affords the BINOL monosilyl ethers 9-11, which can be resolved into the pure enantiomers (A)-9-ll and (7 )-9-11, respectively. Reduction with LiAlFF produces the enantiomerically pure triorgano-H-silanes (A)- and (R)-RPhMeSiH (12, R = /-Pr 13, -Bu 14, /-Bu), respectively (Scheme 2). Tamao et al. have used chiral amines to prepare optically active organosilanes.157... 

To a solution of diol 8 in dichloromethane (0.3 mL) was added pyridine (0.5 mL) and the reaction mixture, cooled to —18 °C, was treated dropwise with 1.2 equiv. of TIPSOTf. During the addition the reaction temperature was carefully controlled. When the starting material was consumed (checked by TLC), the solution was evaporated to dryness to give a residue which was processed by column chromatography on silica gel (petroleum ether/EtOAc, 3 1). Monosilyl ether 9 (146 mg, 95%) was obtained as a glassy solid. 

Silane Alcoholysis. Triethylsilane reacts with alcohols in the presence of metal catalysts to give triethylsUyl ethers. The use of dirhodium(n) perfluorobutyrate as a catalyst enables regioselective formation of monosilyl ethers from diols (eq 6). ... 

In an example of a 2° alcohol being protected in the presence of another 2° alcohol, diol 10 was selectively protected with thexyldimethylsilyl chloride to produce the monosilyl ether 11 (eq 6). Other exan5>les similarly employed thexyldimethylsilyl chloride as the reagent of choice for selective protection... 

Synthesis of dienyl chloride 2.349, the dithiane coupling partner for dithiane aldehyde 2.338, was accomplished in five steps from commercially available cis-2-butene-l,4-diol (Scheme 2.72). To this end, monosilylation of 2.344 as the TBS ether and this allyl alcohol was then oxidized with accompanying Zto E isomerization by PCC [122] to afford the enal 2.346 in 73 % yield. a,]S-unsaturated ester 2.347 was accessed by the Still—Gennari modification [219] of the Homer-Wads worth-Emmons olefination in good yield and selectivity (92 %, Z/E — 16 1). Reduction of the resulting ester 2.347 to produce allyl alcohol 2.348, in turn was chlorinated by treatment with LiCl and methanesulfonyl chloride to furnish the requisite dienyl chloride 2.349. 

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