R-butyldimethylsilyl group

Pyrroles and indoles can be protected with the r-butyldimethylsilyl group by treatment with TBDMSCl and n-BuLi or NaH. Triisopropylsilyl chloride (NaH, DMF, 0°-rt, 73% yield) has been used to protect the pyrrole nitrogen in order to direct electrophilic attack to the 3-position.It has also been used to protect an indole.This derivative can be prepared from the silyl chloride and The silyl protective group is cleaved with Bu4N F , THF, rt or with CF3COOH. 

Let us now give some thought to Myers retrosynthetic analysis of 4 (Scheme 8.1). After a partial clearance of reactive epoxide functionality from within 4, Myers disconnected bond a in compound 5 to yield the partially protected diyne 7 and ketone 6 as possible building blocks. Note how one of the terminal alkyne units in 7 has been retrosynthetically protected with a r-butyldimethylsilyl group to permit regiospecific alkynyl... 

Secondary nitroalkanes are converted into the corresponding silyl nitronates in lower yields and only those with r-butyldimethylsilyl groups are sufficiently stable to be available for the next reaction. Ifow-ever, their fluoride-catalyzed 0-silylnitroaldol addition gives only free nitro alcohols which can be subsequently silylated. 

Selective deprotection of trialkyhilyl ethers. A triisopropylsiloxy group can be retained when a r-butyldimethylsilyl group is removed on treatment with fluorosilicic acid at room temperature. 

Silyl ethers play a very important role as hydroxyl-protecting groups. Alcohols can be easily converted to trimethylsilyl ethers by reaction with trimethylsilyl chloride in the presence of an amine or by heating with hexamethyldisilazane. f-Butyldimethylsilyl ethers are also of considerable use as alcohol-protecting groups. The increased steric bulk of the r-butyldimethylsilyl group improves the... 

Stawinski J., Stromberg, R., Thelin, M., and Westman, E. (1988) Studies on the r-butyldimethylsilyl group as 2-(9-protection in oligonbonucleotide synthesis via the H-phosphonate approach. Nucl. Acids Res. 16, 9285-9298. 

If the chifdl duxilidry in Eq 4 96 is modified by changing MeO into more bulky groups such dS trityl (Tr or r-butyldimethylsilyl (TBS group, an improved asymmetric nitro-olefinddon of ct-alkyl- /- and 5-lactones is possible fEq 4 97) ... 

The same research group also showed that the r-butyldimethylsilyl (TBDMS)-protected 4-substitued 4,5-dihydro-l,2,4-oxadiazol-5-one 192 afforded the alcohol 193 on treatment with ethanolic HC1. Mesylation and treatment of the intermediate with sodium iodide gave the iodofluoroalkenyl-substituted 4,5-dihydro-l,2,4-oxadiazol-5-one 194 (Scheme 26) <2004T10907>. 

Selective silylation of ribonucleosides.2 Only the 5 -hydroxyl group of ribonucleo-sides is silylated by reaction with the reagent in THF in the presence of silver nitrate. On addition of pyridine to the reaction, 2, 5 -disilyl derivatives are formed in 80-90% yield. The actual reagent may be r-butyldimethylsilyl nitrate. Highly selective 3, 5 -disilylation can be achieved in the presence of several silver salts (AgN03, AgC104, and AgOAc) in the presence of either DABCO or 4-nitropyridine N-oxide. 

A-r-Butyldimethylsilyl-A-methyltrifluoroacetamide, CH3CN, 5 min, 97-100% yield.23 This reagent also silylates thiols, amines, amides, carboxylic acids, and enolizable carbonyl groups. 

Et3SiH, cat. Et3N, cat. PdCl2, reflux, 3 h, 80% yield.19 If the reaction is performed in the presence of r-BuMe iH, the r-butyldimethylsilyl carbamate can be isolated because of its greater stability.20 5-Benzyl groups are stable to these conditions, but benzyl esters and benzyl ethers are cleaved.19 A similar procedure has been published, but in this case the benzyl ether is stable to the cleavage conditions."... 

The C.115 amino group was protected as a trimethylsilylethyl carbamate (Me3SiCH2CH2OCONHR), a group that was stable to the synthesis conditions and cleaved by the conditions used to remove the r-butyldimethylsilyl (TBS) ethers. 

Selective oxidation of secondary alcohols.1 This oxidant is almost as effective as PCC, but is less acidic and does not attack r-butyldimethylsilyl ethers. This property allows selective oxidation of a secondary hydroxyl group in the presence of the silyl ether of a primary hydroxyl group. 

Ten years later, a Japanese group led by Oikawa developed a mechanistically related method for the selective debenzylation of substituted benzyl ethers based on the reagent 2,3-dichloro-S,6-dicyanobenzo-quinone (DDQ). In contrast to the trityl tetrafluoroborate reaction, the oxidation proceeds at room temperature in the presence of water. Furthermore, under these convenient and essentially neutral conditions, many functional groups, including other common protecting groups, such as isopropylidine, methoxy-methyl, benzyloxymethyl, tetrahydropyranyl, acetyl, r-butyldimethylsilyl, benzyl, benzoyl and tosyl, are unaffected. As a result of the hig levels of selectivity which can be achieved, this method for the depro-... 

Alcohol 46, after protection with a r-butyldimethylsilyl (TBDMS) group to 47, was converted into amide 48 by aminolysis with 0-benzylhydroxylamine in CHCI3. The amide 48 was desilylated to give N-benzyloxy-(3/ )-hydroxy-butyramide (49), which was converted into l-benzyloxy-(4S)-methyl-2-azeti-dinone (SO), as shown in Scheme 8 (85CC1418). 

There are numerous types of silyl ethers, but r -butyldimethylsilyl- or -diphenylsilyl groups are the most frequently used — mainly due to their suitable stability for oligosaccharide synthesis (i.e., not too acid sensitive). A problem encountered with silyl ethers is that, like esters, they might... 

Spiropentasiladiene 9 is kinetically stabilized by steric protection by four bulky tris(r-butyldimethylsilyl)silyl groups, but the other main reason for the thermal stability is much smaller strain energy (SE) of the ring system than that of the carbon analog. The SE value of the parent spiropentasiladiene SisHi with Did symmetry was calculated to be almost a half of that of the... 

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