TBDMS

NBS, CH3CN, H2O, 62-90% yield.The POM group has been selectively removed in the presence of an ethoxy ethyl ether, TBDMS ether, benzyl ether, p-methoxybenzyl ether, an acetate, and an allyl ether. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

Benzyl, allyl, methyl, THP, TBDMS, and TBDPS ethers are all stable to these conditions. A primary MEM group could be selectively removed in the presence of a hindered secondary MEM group. 

NCSBu2Sn)20 1%, THF, H20. Acetonides and TMS ethers are also cleaved under these conditions, but TBDMS, MTM, and MOM groups are stable. This catalyst has also been used to effect transesterifications. ... 

H2, Pd-C, EtOH, 1 atm, 98-100% yield. This group is stable to 3 M aqueous acetic acid at room temperature, conditions that cleave the TBDMS group and the 1-methyl-1-benzyloxyethyl ether. 

Dichlorodicyanoquinone (DDQ), CH2CI2, H2O, 40 min, it, 84-93% yield.This method does not cleave simple benzyl ethers. This method was found effective in the presence of a boronate. The following groups are stable to these conditions ketones, epoxides, alkenes, acetonides, to-sylates, MOM ethers, THP ethers, acetates, benzyloxymethyl (BOM) ethers, and TBDMS ethers. 

The triethylsilyl ether is approximately 10-100 times more stable than the TMS ether and thus shows a greater stability to many reagents. Although TMS ethers can be cleaved in the presence of TES ethers, steric factors will play an important role in determining selectivity. The TES ether can be cleaved in the presence of a /-butyldimethylsilyl ether using 2% HE in acetonitrile. In general, methods used to cleave the TBDMS ether are effective for cleavage of the TES ether. 

The greater bulkiness of the TIPS group makes it more stable than the /-butyldi-methylsilyl (TBDMS) group, but not as stable as the /-butyldiphenylsilyl (TBDPS) group to acidic hydrolysis. The TIPS group is more. stable to basic hydrolysis than... 

This group is more labile to hydrolysis than the TBDMS group and has been used to protect in alcohol where the TBDMS group was too resistant to cleavage. The DEIPS group is approximately 90 times more stable than the TMS group to acid hydrolysis and 600 times more stable than the TMS group to base-catalyzed solvolysis. 

AcOH, H2O, THE. Any of the methods used to cleave the TBDMS ether also cleave the DEIPS ether. 

TBDMSCl, imidazole, DMF, 25°, 10 h, high yields. This is the most common method for the introduction of the TBDMS group on alcohols with low steric demand. The method works best when the reactions are mn in very concentrated solutions. This combination of reagents also silylates phenols, hydroperoxides, and hydroxyl amines. Thiols, amines, and carboxylic acids are not effectively silylated under these conditions. ... 

TBDMSOSO2CF3, CH2CI2, 2,6-lutidine, 0-25°. This is one of the most powerful methods for introducing the TBDMS group. Other bases such as... 

The following schemes represent some interesting examples where the TBDMS group is introduced selectively on compounds with more than one alcohol. 

Aqueous HF, CH3CN (5 95), 20°,. 1-3 h, 90-100% yield. This reagent will cleave ROTBDMS ethers in the presence of ArOTBDMS ethers. This reagent can be used to remove TBDMS groups from prostaglandins. 

LiBF4, CH3CN, CH2CI2, 40-86% yield.In this case Bu4N F or acid failed to remove a primary TBDMS group from a steroid. 

Selectivity in the cleavage of a primary allylic TBDMS group was achieved with HF/CH3CN in the presence of a more hindered secondary TBDMS group. ... 

Selective cleavage of one secondary TBDMS ether in the presence of a somewhat more hindered one was achieved with Bu4N F in THF. ... 

Pyridinium p-toluensulfonate, EtOH, 22-55°, 1.2-2 h, 80-92% yield. These conditions were used to leihove cleanly a TBDMS group in the presence of a TBDPS group. 

AC2O, CH2CI2, 15 kbar (1.5 GPa), 79-98% yield. This high pressure technique also works to introduce benzoates and TBDMS ethers onto highly hindered tertiary alcohols. 

TsOH, DMF, Mc2C(OMe)2, 24 h. This method has become one of the most popular methods for the preparation of acetonides. It generally gives high yields and is compatible with acid-sensitive protective groups such as the TBDMS group. 

Me2C(OMe)2, DMF, pyridinium p-toluenesulfonate (PPTS). The use of PPTS for acid-catalyzed reactions has been quite successful and is particularly useful when TsOH acid is too strong an acid for the functionality in a given molecule. TBDMS groups are stable under these conditions. 

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

Dimethyl sulfoxide, 180°, H2O, 10 h, 89% yield.A diethyl acetal can be cleaved in the presence of a 1,3-dioxolane under these conditions. TBDMS, THP, and MOM groups are stable. 

HS(CH2) SH, BF3-Et20, CH2CI2, 25°, 12 h, high yield, n = 2, n = 3. In a,/3-unsaturated ketones the olefin does not isomerize to the /3,7-position as occurs when an ethylene ketal is prepared. Aldehydes are selectively protected in the presence of ketones except when steric factors force the ketone to be protected as in the example below." A TBDMS group is not stable to these conditions. ... 

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