Selective cleavage 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. 

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

A highly selective and mild procednre for cleavage of TBDMS ethers to the corresponding alcohols by nsing Oxone was developed recently. Interestingly, it has been found that feri-butyldiphenylsilyl (TBDPS) ether and certain acid-labile gronps snch as tetrahydropy-ranyl (THP), A-Boc or a carbon-carbon donble bond remain nnaffected under the reaction conditions (eqnation 69) . ... 

The selective cleavage of the IV-t-butoxycarbonyl group in the presence of TBDMS (t-butyldimethylsilyl) (selective only when the protected alcohol was phenolic) or TBDPS (ferf-butyldiphenylsilyl) (completely selective) ethers can be achieved68 using a saturated solution of HC1 in ethyl acetate. 

Tetrahydropyranyl (THP) ethers, another species known to be unstable to acid, have similarly been reported to be cleaved by solutions of iodine in methanol.209 At room temperature, cleavage of the THP ethers was complete in 1.5 to 8 h. As with the previous example using iodine in methanol at lower than reflux temperature, TBDMS ethers were stable to these conditions. The ability to tune the reactivity of the iodine in methanol system by simply controlling the temperature is of value in selective deprotection. This is even more useful when fluorine, known to remove only silyl ethers,105 is exploited. Given that methoxymethyl ethers, essentially acetals, are known to be cleaved under acidic conditions, it seems likely they too should be subject to removal by solutions of iodine in methanol. Sundry examples of deprotections using iodine in methanol are presented in Table IV. 

TBDPS ether is visible under UV light and thus it is more advantageous than the corresponding TBDMS ether if there is no chromophore present in the alcohol. Selective protection of the primary alcohol can be achieved as shown below. Silyl chloride and cleavage by-product silylol are both lachrymators and therefore the reactions should be carried out in the hood. The procedures for protection and cleavage are applicable to other silyl ethers such as ferf-butyldimethylsilyl, trimethylsilyl, and tri-isopropylsilyl. 

DMSO, H2O, 90°C, 82% yield. Selective cleavage of a phenolic TBDMS ether occurs in the presence of the alkyl ether. ... 

Primary TBDMS ethers can be cleaved selectively in the presence of THP ethers and ketals using ceric ammonium nitrate in methanol. Both phenolic and aliphatic TBDMS ethers undergo cleavage when exposed to catalytic amounts of PdCl2(MeCN)2 in the latter case, and with longer exposure, this also results in oxidation to the corresponding aldehyde or ketone, if the alcohol was primary or secondary, respectively. This cleavage and oxidation can be performed selectively in the presence of TIPS, TBDPS and benzyl ethers (equation 15). 

In the synthesis of a building block for the use of 7-deazaadenosine (tubercidin) in solid phase oligoribonucleotide synthesis, a tri-isopiupylsilyl ether could be introduced at 0-2 with good selectivity,2 and the Tbdms group has been placed mito 5 -0-Dmtr-2 -deoxynucleosides using NaH and dibenzo[18]ciDwn-6. Cleavage of Tbdms ethers from nucleotides has been carried out 1 ads( btion rmto neutral alumina and use of a nticrowave oven. ... 

Furthermore, several functionalities remained unaffected, namely the acid-labile TBDMS or PMB groups.118 Deprotection yields were in the range of 85-95% when methanol was used at room temperature as the solvent, whereas acetonitrile or dichloromethane led to very sluggish or nonexistent reactions, respectively. Cleavage of primary trityl ethers was also accomplished using the same conditions in a very rapid and effective fashion. The trityl pyranosides and furanosides assayed were selectively deprotected in 2-3 h and yields higher than 85% were achieved. This reaction was also more efficient when conducted in methanol, which acts as a nucleophile to trap the generated trityl cation. 

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