Dimethylsilyl ethers

Hydroxystyryl)dimethylsilyl Ether (HSDMS-OR) and (2-Hydroxystyryl)diisopropylsilyl Ether (HSDIS-OR)... 

A/ HE, 0.1 M NaF, pH 5. THE, 25°, 2 days, 77% yield. In this substrate, a mixture of products resulted from the attempted cleavage of the t-butyl-dimethylsilyl ether with tetra-n-butylammonium fluoride, the reagent generally used. ... 

Compound 158 is the starting material. This compound is first reduced with sodium borohydride to 159, and the resulting hydroxyl group is then protected as its tert-butyl dimethylsilyl ether (Scheme 7 49). The resulting compound 160 appears to possess the C-ring skeleton of baccatin HI. 

Protection of Alcohols. Trimethylsilyl ethers, readily prepared from alcohols by treatment with a variety of silylating agents have found considerable use for the protection of alcohols. They are thermally stable and reasonably stable to many organometallic reagents and they are easily cleaved by hydrolysis in acid or base or by treatment with fluoride ion. t, Butyl dimethylsilyl ethers have considerably greater hydrolytic stability and are easier to work with than trimethylsilyl ethers. They are prepared from alcohols by treatment with t. butyl dimethylsilyl chloride. 

The generality of these observations is supported by the data in Scheme 8. In the case of the reactions of monosubstituted l-(l-alkynyl)cyclopropanols 15, 5-substituted cyclopentenones 17 are obtained with complete selectivity when trans-15 are used as substrates. On the other hand, 4-substituted cyclopentenones 16 are obtained with good to high regioselectivity by employing ferf-butyl-dimethylsilyl ethers of cis-l5 as substrates. Furthermore, 5,5-disubstituted cyclopentenones 20 including a spirocyclic derivative are obtained selectively starting from 2,2-disubstituted l-(l-alkynyl)cyclopropanols 18. 

Although several advantages of dimethylsilyl (Me2HSi) ethers have been claimed,191 few examples of their use have been reported, except for the separation of cycloamyloses.133 Thus, dimethylsilyl derivatives (which are more volatile than trimethylsilyl ethers) require lower column-temperatures and have shorter retention times for example, for glucose, the per(trimethylsilyl) derivative has a retention time of 11.4 min, and the per(dimethylsilyl) derivative, 5.10 min. Both types of derivative may be analyzed on the same column, and, in certain cases, compounds inseparable as their O-trimethylsilyl derivatives may be separated as their dimethylsilyl ethers. The potential of di-methylsilylation for converting oligosaccharides into volatile derivatives should be examined. 

Intramolecular free radical reactions have been also exploited using silicon temporary attachment [97]. Reduction of enone 134, gave the corresponding allylic alcohol, which is transformed into the bromomethyl-(dimethylsilyl) ether 137 (Scheme 47). Radical cy-... 

N-(trimethylsilyl)imidazole, is particularly useful in the presence of water and reacts virtually quantitatively with glucose in 50% water solutions (75). Dimethylsilyl ethers generated from (CHj SiHCl have also been suggested and provide greater... 

Use of the related dimethylsilyl ethers, obtained from (3-hydroxy ketones using commercially available chlorodimethylsilane, affords 4 with only slightly less dia-stereoselectivity. Other Lewis acids can be used in place of SnCLj.1... 

Intramolecular hydrosilylations of functionalized alkenes followed by hydrogen peroxide oxidation provide powerful methods for organic syntheses86-88. The reactions of allylic O-dimethylsilyl ethers 59 promoted by platinum catalysts, e.g. Karstedt s catalyst and Pt(PPh3)2(CH2=CH2), or rhodium catalysts, e.g. Rh(acac)(COD) and [RhCl(CH2=CH2)2]2> proceed via 5-endo cyclization to give oxasilacyclopentanes 60 with a couple of exceptions in which siloxatanes 61 are formed (Scheme ll)87,89. 

Enaminoketoesters were reacted with benzyl chloroformiate in the presence of sodium hydride to furnish the /V-protected enaminoketoesters. The reduction of the carbonyl group with NaBkLt in methanol was followed by transformation of the derived hydroxyl group into the corresponding ferf-butyl dimethylsilyl ether by... 

Quilliam, M.A., Ogilvie, K.K., Sadana, K.L., and Westmore, J.B., Study of rearrangement reactions occurring during gas chromatography of tert-butyl-dimethylsilyl ether derivatives of uridine, J. Chromatogr., 194, 379, 1980. 

Octakis (2,3,6-tri-0-methyl-gamma-cyclodextrin) was used to separate enantiomers of methyl esters of deltametrinic acid and permetrinic acid the positional isomers of nitrotoluene were also separated on the same column [17,18]. Various alkyl- and dialkyl-benzenes have been separated on beta- and gamma-cyclodextrin [19]. A complete review of the use of cyclodextrins in chromatography has been published by Hinze [20]. Cyclo-dextrins have been analyzed by packed-column gas chromatography as their dimethylsilyl ethers [21]. 

J. Beadle, Analysis of cyclodextrin mixtures by gas chromatography of their dimethylsilyl ethers, J. Chromatogr., 42 201-206 (1969). 

In addition to TMS ethers, dimethylsilyl ethers [36] were studied for the analysis of alcohols and phenols. They were prepared by reaction with reagents analogous to those used for TMS ethers [dimethylmonochlorosilane and tetramethyldisilazane in pyridine (1 3 9)] and they provide shorter retention times in comparison with TMS ethers on Apiezon L. Grant [37] converted phenols into bromomethyldimethylsilyl ethers. In addition to a higher sensitivity, selective detection, permitting, e.g., phenolic substances to be determined in tars without any preliminary separation, was even achieved by using an ECD. 

Highly diastereoselective 7-rro/o-radical cyclization of (bromomethyl)dimethylsilyl ethers 150, derived from ethyl y-hydroxy-a-methylenecarboxylates, bearing a bulky y-substituent such as isopropyl, cyclohexyl, and tert- mty in THF gave cyclic silyl ethers 151 bearing preferentially the ethoxycarbonyl group anti to the y-substituent (Equation 28) <2004TL4329>. 

Chromatography.—Considerable attention is being paid to chromatographic methods for the separation and recognition of bile acids and their derivatives. The analysis (g.l.c.) of mixtures of bile acids and their conjugates is reported to be simplified by direct conversion into heptafluorobutyrate derivatives, which occurs with simultaneous deconjugation.The carboxyl function is apparently converted into its volatile mixed cholanyl-heptafluorobutyryl anhydride. Ethyl-dimethylsilyl ethers of bile acid ethyl esters are also reported to be suitable for... 

While often considered undesirable pathways in the past, radical hydrogen transfers have also been shown to constitute intriguing possibilities for organic synthesis. Curran has for instance defined the concept of protection and radical translocation (PRT) groups, fii this context, 2-0-(2-bromo-aryl)dimethylsilyl ethers, aryl amides and 2-bromo-4-methoxyphenyl ethers... 

Novel derivatives for gas-chromatographic analysis of steroids, with electron-capture detectors, include (halogenomethyl)dimethylsilyl ethers (778), penta-fluorobenzoates, methyl hemiacetals (779) derived from steroid alcohols and dichlorotetrafluoroacetone, and dienol heptafluorobutyrates, readily obtained from 4-en-3-ones. ... 

Chart 1, may be used for a synthesis of verrucarinic acid 21 as outlined in equation 6 the acid is produced as its bis t-butyl-dimethylsilyl ether for incorporation into verrucarin A J8). 

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