T-Butyldimethylsilyl

The C.115 amino group was protected as a trimethylsilylethyl carbamate (Me3SiCH2CH20C0NHR), a group that was stable to the synthesis conditions and cleaved by the conditions used to remove the t-butyldimethylsilyl (TBS) ethers. 

SEM ethers are stable to the acidic conditions (AcOH, H2O, THE, 45°, 7 h) that are used to cleave tetrahydropyranyl and t-butyldimethylsilyl ethers. 

NaH, HMPA, 0°, 5 min H2O, 83-84% yield. These conditions selectively cleave a TBDPS ether in the presence of a t-butyldimethylsilyl ether. 

AC2O, FeCl3, rt, <30 min, 60-93% yield. These conditions selectively protect an aldehyde in the presence of a ketone." This combination also converts t-butyldimethylsilyl (TBDMS) ethers to acetates. 

The above mechanism involves a-opening of the epoxysilane, followed by a 1,2-elimination of a /3-hydroxysilanc (Peterson olefination, Chapter 10). However, it has recently been shown that aj8-dihydroxysilanes, particularly t-butyldimethylsilyl species, undergo an acid-catalysed sila-pinacol rearrangement to produce /J-aldehydo- and /i-kctosilancs (5) ... 

Conversion of allyl alcohol esters into their corresponding trimethylsilyl or t-butyldimethylsilyl ketene acetals, followed by mild thermolysis, results in... 

The same coordination is used to account for the observed anti preference in the allylation of (t-hydroxybutanal with allyl bromide/indium in water (Scheme 8.16). The intermediate leads to the anti product. In support of the intramolecular chelation model, it is found that if the hydroxy group is converted to the corresponding benzyl or t-butyldimethylsilyl ether, the reaction is not stereoselective at all and gives nearly equal amounts of syn and anti products. 

Optically active /3-ketoiminato cobalt(III) compounds based on chiral substituted ethylenedi-amine find use as efficient catalysts for the enatioselective hetero Diels Alder reaction of both aryl and alkyl aldehydes with l-methoxy-(3-(t-butyldimethylsilyl)oxy)-1,3-butadiene.1381 Cobalt(II) compounds of the same class of ligands promote enantioselective borohydride reduction of ketones, imines, and a,/3-unsaturated carboxylates.1382... 

A zinc-mediated carbon-carbon coupling reaction can be carried out on the metallated form of (t-butyldimethylsilyl)(2-pyridylmethyl)amine, formed in reaction with dimethylzinc. The isolated dimeric species can be reacted with further dimethyl zinc to give bis(methylzinc)-l,2-dipyridyl-l,2-bis(t-butyldimethylsilylamido)ethane, which contains two N3C coordinated zinc centers.89... 

If the chiral auxiliary in Eq. 4.96 is modified by changing MeO into more bulky groups such as trityl (Tr) or t-butyldimethylsilyl (TBS) group, an improved asymmetric nitro-olefination of a-alkyl-y- and 8-lactones is possible (Eq. 4.97).120... 

Figure lZpl Total synthesis of (-)-Pateamine A.TBS, t-butyldimethylsilyl TIPS, triisopropyl silyl TCBoc, trichloro t-butoxycarbamate DIAD, diisopropyl azodicarboxylate. 

A variety of alcohols, protected as t-butyldimethylsilyl (TBDMS) ether derivatives, can be rapidly regenerated to the corresponding hydroxy compounds on alumina surface using MW irradiation (Scheme 6.8) [42], This approach prevents the use of corrosive fluoride ions that are normally employed for cleaving the silyl protecting groups. 

A nickel-chromium catalyst prepared from chromous chloride and (p-diphenylphos-phinopolystyrene)nickel dichloride mediates the ring-closure of the ene-allene 236 (R = H) to a mixture of 3.4 parts of 237 and 1 part of 238 (equation 120)121. An analogous reaction of the t-butyldimethylsilyl ether of 236 yields solely the (E)-isomer 237 (R = t-BuMeaSi). Cyclization of the ene-allene 239 affords the perhydroindane 240 in 72%... 

Li et al.39 reported the hetero Diels-Alder reaction of alkyl-3-(t-butyldimethylsilyl) oxy-1,3-butadiene 95 with ethyl glyoxylate 96 in the presence of a salen-Co(II) catalyst 94 (2 mol%). Product 97 was obtained in 75% isolated yield with an endo. exo ratio >99 1. The enantiomeric excess of the endo-iorm was up to 52% (Scheme 5-30). 

Reduction of benzyl ethers. Benzyl ethers are cleaved in high yield by calcium (2 equiv.) in liquid ammonia. By proper control of the amount of metal, selective reduction of benzyl ethers is possible in the presence of a triple bond or a t-butyldimethylsilyl ether group. However, there is little selectivity between benzyl ethers and thiophenyl, epoxide, or keto groups in this reduction. 

Scheme 9.6 Synthesis of methyl heptaglucoside 1. The letters indicate intermediates used in the synthetic sequence displayed at the bottom of the scheme. The numbers describe reaction conditions or reagents (1) IV-iodosuccinimide, trifluoroacetic acid (2) removal of benzylidine (3) acetylation (4) removal of t-butyldimethylsilyl (5) sodium methoxide/methanol.

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