Tert-butyldiphenylsilyl ether

M. T. Barros, C. D. Maycock, F. Sinerez, and C. Thomassigny, Fast galloylation of a sugar moiety Preparation of three monogalloylsucroses as references for antioxidant activity. A method for the selective deprotection of tert-butyldiphenylsilyl ethers, Tetrahedron, 56 (2000) 6511-6516. 

Table 7 Stability Characteristics of Trimethylsilyl, tert-Butyldimethylsilyl, and tert-Butyldiphenylsilyl Ethers of Serine, Threonine, and Hydrox5 proline[ - - - l...

Adoption of the Diels-Alder approach depicted requires that the eventual C(9) configuration be inverted at some point in the synthesis and that the six-member B ring undergo ring contraction. Prior to addressing these two issues, the hydroxyl group in (302) was protected [TBDPSC1, imidazole, DMF, 70%] as its tert-butyldiphenylsilyl ether (303). 

The Cram chelation model (sec. 4.7.B) is an example where the chelation effects of the heteroatom influence the rotamer population and, thereby, the selectivity of the reduction. Zinc borohydride [Zn(BH4)2], effectively chelates the carbonyl oxygen and alcohol oxygen atoms in the reduction of 42 and leads to intermediate 43. Transfer of hydride to the carbonyl gave primarily the anti diastereomer, 45 (4 96, 44/45). When the chelating hydroxyl group was blocked as a tert-butyldiphenylsilyl ether (in 46 - sec. 7.3.A.i), reduction with Red-Al (sec. 4.3) led to a reversal in selectivity (96 4, 47/48).The ability to chelate a heteroatom varies with the reagent used. Lithium aluminum hydride shows less selectivity, due in part to poorer coordination with the heteroatom and reduction of 42 gave a 27 73 mixture of 44 and 45,... 

Cleavage of Protecting Groups. THP ethers of primary, secondary, and phenolic alcohols can be conveniently de-protected at room temperature by treatment with 1.2 equiv of TMSOTf in methylene chloride (eq 96). Deprotection of tert-butyldimethylsilyl ethers in the presence of a tert-butyldiphenylsilyl ether has been smoothly accomplished using TMSOTf at —78°C, as one of the steps of the total s)mthesis of marine macrolide ulapualide A. ... 

In the same year, Teo and Chua reported that L-serine tert-butyldiphenylsilyl ether efficiently catalyzed an asymmetric aldol reaction between cycloalkanones and aromatic aldehydes in [bmim][BF4] [40]. The catalyst solution in the IL withstood three recovery cycles however, a progressive decrease of activity caused by the leaching of the siloxy serine catalyst from the IL medium to the ether solution used for extraction of products and a slight decline of reaction enantioselectivity were recorded. 

Tin-based reagents are not always snitable owing to the toxicity of organotin derivatives and the difficulties often encountered in removing tin residues from the final product. Therefore, the same authors have carried out additional experiments with 17d and several different alkyl halides under tin-free conditions. The treatment of 16d with tert-butyldiphenylsilyl chloride (TBDPSCl) and triethylamine in the presence of silver triflate in CH2CI2 affords the bis(silyloxy)enamine 17d in 92% yield (Scheme 17). When the radical reaction was carried out with ethyl iodoacetate in the presence of 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator in CH2CI2, the oxime ether 19 was obtained in 83% yield (Scheme 17). 

The dependence of the acid-lability of trialkylsilyl and related ethers on the type of substitution at silicon is illustrated by the formation302 of l-0-(tert-butyldiphenylsilyl)-2,3 4,5-di-0-methylene-D-mannitol (47) in 96% yield on treatment of 6-0-(terf-butyldimethylsilyl)-l-0-(fert-butyldiphenylsilyl)-2,3 4,5-di-O-methylene-D-manni-tol (48) with 80% acetic acid. 

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 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 . 

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. 

Retention of configuration. A soln. of BBr3 in methylene chloride added to a soln. of (R)-(-)-2-octyl rr-butyldimethylsilyl ether in the same solvent at 0°, stirred at room temp, for 10 min, and treated with satd. NaHC03 - (-)-2-bromooctane. Y 90% (71% retention of configuration). With Ph3PBr2 (Synth. Meth. 42, 480) reaction proceeds with inversion of configuration. Tert., sec., benzylic and allylic silyl ethers were cleaved more rapidly than prim, silyl ethers. With allylic ethers, double bond shift takes place. F.e. inch cleavage of rr-butyldiphenylsilyl ethers s. S. Kim, J.H. Park, J. Org. Chem. 53, 3111-3 (1988). 

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