Terf-butyldimethylsilyl ethers

Silica gel-based catalytic systems have been described as efficient promoters for a number of organic reactions.28 Illustrative examples include the oxidative cleavage of double bonds catalyzed by silica-supported KM11O4,29 reaction of epoxides with lithium halides to give /i-halohydrins performed on silica gel,30 selective deprotection of terf-butyldimethylsilyl ethers catalyzed by silica gel-supported phosphomolybdic acid (PMA),31 and synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts.32... 

Just as the terf-butyldimethylsilyl ethers are used as protecting groups for alcohols (Section 20.12), acetals are valuable protecting groups for aldehydes and ketones. 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

Deprotecting a terf-butyldimethylsilyl ether to re-form an alcohol... 

As depicted in Fig. 6, syntheses of enantiomerically pure 116 and 117 have been carried out [236]. Lipase AK-catalysed asymmetric acetylation of meso-2,4-dimethyl-1,5-pentanediol A yielded (2R,4S)-5-acetoxy-2,4-dimethylpen-tanol B. Protection of the free hydroxy group as the terf-butyldimethylsilyl (TBS) ether, saponification of the acetate, and oxidation furnished the aldehyde C. Reaction of C with ethylmagnesium bromide gave a diastereomeric mixture of the corresponding secondary alcohols which could be resolved by asym-... 

The dependence of the acid-lability of trialkylsilyl and related ethers on the type of substitution at silicon is illustrated by the formation302 of l-0-(tert-butyldiphenylsilyl)-2,3 4,5-di-0-methylene-D-mannitol (47) in 96% yield on treatment of 6-0-(terf-butyldimethylsilyl)-l-0-(fert-butyldiphenylsilyl)-2,3 4,5-di-O-methylene-D-manni-tol (48) with 80% acetic acid. 

In a process related to GTP, aldehydes initiate the polymerization of silyl vinyl ethers and silyl diene ethers. Here the silyl group is present in the monomer and transfers to the aldehyde ended chains regenerating aldehyde ends [17] (Scheme 8). A Lewis acid catalyst is required. terf-Butyldimethylsilyl works best as a transfer group for vinyl ether while trimethylsilyl is suitable for diene ethers [18]. Even though aldol GTP provides a route to polyvinyl alcohol segments in the subsequent block polymer synthesis, the projected cost of the monomers discouraged further research aimed at commercialization. 

SiVE 2 - [ (terf-butyldimethylsilyl) oxy] ethyl vinyl ether... 

Temporary stereogenic centers derived from optically active a-silylallylic alcohols can serve as a chiral primary alcohol equivalent, Thus, the benzyl ethers 12 and 13 are prepared by rearrangement of 11 followed by protodesilylation478. The racemic a-silyl alcohol moiety of 11 is obtained by Brook rearrangement of the terf-butyldimethylsilyl crolyl ether479. 

When the alkenyl component is an O-terf-butyldimethylsilyl (TBDMS) enol ether, another anomaly occurs independent of enol ether geometry, the anti product is favored (Scheme 6.8) [62]. With trimethylsilylpropargyl ethers, the anti selectivity is 95-98%, making this reaction an excellent route for the preparation of anti 1,2-diols. In these cases, transition structures similar to Figure 6.6c and d are operative, the dominant influence being mutual repulsion between the carbanion substituent, R, and the 0-silyl group. 

If the living ROMP of norbomene is terminated with a nine-fold excess of terephthalaldehyde, the chains formed cany an aldehyde end-group, which, when activated by ZnCl2, can be used to initiate the aldol-group-transfer polymerization of terf-butyldimethylsilyl vinyl ether (Risse 1989a, 1991). 

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