Butyldiphenylsilyl TBDPS Ethers

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) . ... 

Silyl ethers, such as TMS, triethylsilyl (TES), triisopropylsilyl (TIPS), lerl-butyldi-methylsilyl (TBS), and terl-butyldiphenylsilyl (TBDPS) ethers (Scheme 2.6), are frequently used in carbohydrate chemistry due to their unique reactivity and steric effect (see Section 2.4.1) [1, 2], These groups are typically introduced onto the molecule by treatment with the corresponding silyl halide or triflate (OTf) and a base, such as Et3N, pyridine, 2,6-lutidine, or imidazole. 

Reaction of 4-(pivaloyloxy)benzaldehyde with the E -crotyldiisopinocampheylbo-rane d19E gave the corresponding homoallylic alcohol 22 in a 98 2 enantiomeric ratio. After protection of the alcohol as a tert-butyldiphenylsilyl (TBDPS) ether, the alkene was subjected to ozonolysis to provide the 3-hydroxy aldehyde 23. 

The mildest reagent for cleaving TBS ethers is pyridinium p-toluenesulfonate (PPTS) in a protic solvent — usually methanol. Under these conditions a primary TBS ether can be cleaved in the presence of a 2-(trimethylsilyl)ethoxy-methyl (SEM) ether and 2-(trimethylsilyl)ethyl ester [Scheme 4.26]. Primary TBS ethers cleave at room temperature but secondary TBS ethers may require elevated temperature. In the transformation shown in Scheme 4.27 two TBS ethers were cleaved in the presence of a TIPS ether." rerf-Butyldiphenylsilyl (TBDPS) ethers are impervious to attack under these conditions as evinced by the selective removal of a primary TBS ether in the presence of an equally exposed primary TBDPS ether in a synthesis of NodRm-IV factors, glycolipids produced by symbiotic fungi that elicit formation of nitrogen-fixing root nodules in legumes [Scheme 4.28]. ... 

Silyl ethers, including tert-butyldimethylsilyl (TBS) ethers (Section 11.HE) and phenyl-substituted ethers, are also used as protecting groups in carbohydrate synthesis. tert-Butyldiphenylsilyl (TBDPS) ethers show excellent regioselectivity for primary hydroxyl groups in sugars, such as at C6 in a hexopyranose. 

Two new procedures have appeared for the regeneration of alcohols from their TBDMS ethers, using either NBS in aqueous DMSO (a cheap and easy alternative) or a tetrafluoroborate salt (lithium or trityl). The tri-isopropylsilyl (TIPS) group has been examined as a protecting function for hydroxy-groups. TIPS ethers are found to be intermediate in stability towards acid hydrolysis between TBDMS ethers and the more resistant t-butyldiphenylsilyl (TBDPS) ethers. Base hydrolysis is slower than in acid, and TBDPS ethers now react more rapidly than TIPS ethers. Not surprisingly the TIPS group may be removed by fluoride ion. 

The synthetic potential of silyl ethers as protecting groups for hydroxyls is based on the fact that they can be easily introduced and cleaved under mild conditions and their relative stability can be tuned by varying the substituents on silicon. In carbohydrate chemistry, the tert-butyl-dimethylsilyl (TBDMS), terl-butyldiphenylsilyl (TBDPS) and triethyl-silyl (TES) ethers are the most often applied silicon-based protecting groups (Scheme 2.9).23... 

Mulzer and Schollhorn showed that the reaction of triol monosilyl ether 279 with potassium carbonate gave a 6 7 87 mixture of 279, 280 and 281 at equilibrium (equation 176), indicating that the terminal primary position was favored as the location of the t-butyldiphenylsilyl (TBDPS) group. Similarly, 282 afforded 283 as a major migration... 

The absolute stereochemistry of 20 was determined using the modified Mosher s method [7]. Reduction of 20 with LiAlELt followed by TBDPSCl (tert-butyldiphenylsilyl chloride)/imidazole gave TBDPS ether 20A, Fig. (16). Treatment of 20A with (K)- and (5)-MTPACl gave (R)-and (5)-MTPA esters, 20B and 20C, respectively. The results, as shown in Fig. (16), established that the configuration at C3 was 35. Therefore, the absolute stereochemistry of haterumadioxin A (20) was determined to be 35, 6R and 8i . 

In this section, the formation and cleavage of eight protecting groups for alcohols and phenols are presented acetate acetonides for diols benzyl ether para-methoxybenzyl (PMB) ether methyl ether methoxymethylene (MOM) ether ferf-butyldiphenylsilyl (TBDPS) silyl ether and tetrahydropyran (THP). 

Zert-Butyldiphenylsilyl (TBDPS) protection is one of the most popular alcohol protective groups. It is more stable than other silyl ethers under acidic conditions. 

Bismuth(III) chloride in acetonitrile has been reported as a catalyst for the selective and efficient cleavage of trityl ethers. THP ethers, tert-butyloxicarbonyl (BOC) group, tert-butyldiphenylsilyl (TBDPS) and p-methoxybenzyl (PMB) esters were resistant to these conditions [100]. 

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