Terf-butyldimethylsilyl

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... 

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. 

The category Id cyclization has also been applied to 4-aminoindoles of the type found in the indolelactam tumour promoters such as lyngbyatoxin A and pendolmycin. In a synthesis of analogues of lyngbyatoxin A the isoxazoline 8.4A was constructed as a key intermediate ]. Reductive cleavage of the isoxazoline ring generated 8.4B which was cyclized by reaction with terf-butyldimethylsilyl triflate (Entry 6, Table 8.1). The cyclization of a thioamide was a key step in the synthesis of pendolmycin[5] (Entry 7, Table 8.1). 

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. 

The isocyanide method of reduction has been applied successfully for preparing a series of diversely protected 1,4-anhydroalditols 188 l,4-anhydro-5-O-tert-butyldimethylsilyl-2,3-0-isopropylidene-D-ribitol (56, 81%), l,4-anhydro-5-0-terf-butyldimethylsilyl-6-deoxy-2,3-0-isopropylidene-D-allitol (57,87%) and -l-talitol (58,87%), 1,4-anhydro-2- 0-rert-butyldimethylsilyl-3,5- 0 -isopropylidene-... 

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

FIGURE 5.5 Oxazinone-protected sialoside donors. TBS, terf-butyldimethylsilyl. 

NT0-Bis(terf-butyldimethylsilyl)acetaniide silylates tertiary and hindered secondary alcohols in the presence of a catalytic amount of TBAF or another source of fluoride anion [Scheme 4.67].113 Protection of primary hydroxyl groups in the presence of secondary ones and secondary in the presence of tertiary is possible but the monoprotection of 1,2-diols fails due to the migration of the silyl group caused by the presence of basic fluoride anion. 

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. 

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