Ethers, f-butyldimethylsilyl

Bu4N F, THF, 0°, 1 h, 52-95% yield. A primary alcohol protected as the f-butyldimethylsilyl ether was cleaved under these conditions, but a similarly protected secondary alcohol was stable. 

SEM ethers are stable to the acidic conditions (AcOH, H20, THF, 45°, 7 h) that are used to cleave tetrahydropyranyl and f-butyldimethylsilyl ethers. 

NaH, HMPA, 0°, 5 min H20, 83-84% yield.11 These conditions selectively cleave a TBDPS ether in the presence of a f-butyldimethylsilyl ether. 

Rexyn 101 (polystyrene sulfonic acid), 80-91% yield.38 This method does not cleave the f-butyldimethylsilyl ether. 

Cleavage of tetrahydropyranyl ethers.16 Tetrahydropyranyl ethers are cleaved to the alcohol by dimethylaluminum chloride or methylaluminum dichloride in high yield at temperatures of -25 to 25°, conditions that do not affect f-butyldimethylsilyl ethers. MOM and MEM ethers are converted into ethyl ethers by a methyl transfer reaction. 

Cleavage of MOM ethers, Methoxymethyl ethers are cleaved by this reagent at 0° in 80-97% yield. Acetals and THP, trityl, and f-butyldimethylsilyl ethers also are cleaved, but less readily.2... 

OL-PhenylseUno aldehydes. Oxidation of allylic f-butyldimethylsilyl ethers remits in a-phenylseleno aldehydes, which on desilylation give a-phenylseleno-a,/9-unsaturated enals. A typical example is formulated in equation (I). 

On the other hand, unsaturated aldehydes and ketones were obtained using allylic alcohols as alkene components [68]. Similarly, allyl f-butyldimethylsilyl ether and N-allylamides gave silyl enol ethers [69] and enamides [70], respectively. The ruthenium-catalyzed alkene-alkyne coupling was successfully combined with the palladium-catalyzed intramolecular asymmetric allylic alkylation [71] to provide a novel one-pot heterocyclization method [72]. 

Diastereomeric mixtures of vicinal nitro alcohols obtained by a classical Henry reaction with low dia-stereoselectivity can be easily silylated to give the corresponding mixture of 0-f-butyldimethylsilyl ethers. The latter undergoes an enrichment of the erythro isomer (54 up to >95 5) by treatment with LDA and successive protonation of the corresponding lithium salts (Scheme 8), which occurs with high diastereoselectivity. 

Although alkylation of 3-hydroxy ester dianions occurs with high diastereofacial selectivity, the aldol reaction of the dianion obtained from methyl 3-hydroxybutanoate with benzaldehyde gives all four dia-stereomeric aldols in a ratio of 43 34 14 9 (equation 117).155 On the other hand, dianions of 8-hydroxy esters show rather good diastereofacial preferences under the proper conditions. Deprotonation of t-butyl-5-hydroxyhexanoate with lithium diethylamide in the presence of lithium triflate gives an enolate that reacts with benzaldehyde to give aldols (196) and (197) in a ratio of 91 9 (equation 118).156 Use of the f-butyldimethylsilyl ether instead of the alcohol resulted in no facial preference. 

Desilylation. A solution of Oxone in 50% aq MeOH is effective for cleaving primary and aromatic f-butyldimethylsilyl ethers at room temperature. In a molecule containing both types of ethers, the aliphatic silyl group can be selectively removed by virtue of the faster rates of hydrolysis. 

A synthesis of unsymmetrical azines is based on the formation of trisiopropylsilylhy-drazones and their reaction with different carbonyl compounds in the presence of BU4NF. A combination of BU4NF and HOAc selectively cleaves f-butyldiphenylsilyl ethers without affecting f-butyldimethylsilyl ethers. ... 

Cleavage of TBS ethers. f-Butyldimethylsilyl ethers of both phenols and aliphatic... 

Scheme 8.80. A representation of the pathway from the f-butyldimethylsilyl ether of the enol of cyclohexanone to 2-methylcyclohexanone via the addition of methylene from the Simmons-Smith reagent and rearrangement of the cyclopropane formed (see Simmons, H. E. Smith, R. D. J. Am. Chem. Soc., 1959,81,4256).

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... 

Functional groups sometimes sensitive to acidic conditions such as simple esters, " lactones,acetals, epoxides, 2-methoxyethyloxymethyl (MEM) groups, f-butyldimethylsilyl ethers, " and orthoformates are generally unaffected by the catalytic amounts of acid used, although some tertiary alcohols and l-trimethylsilylalkynes have been noted to give poor yields. 

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