1 - Dimethyl- -silyl

Fig. 37. Resist images obtained with a cross-linking monocomponent TSI resist (PHOST polymer), cross-linked by photo-oxidation using light at 193-nm wavelength. After exposure, the film was treated with a vapor of dimethyl silyl dimethyl amine and then plasma developed using O2—RIE (122).

StericaHy hindered silyl ethers such as ferZ-hutyl dimethyl silyl, / fZ-butyldiphenylsilyl, and tricyclohexylsilyl have been proposed as alternatives to trityl ethers. Reaction of sucrose with 3.5 molar equivalents of ferZ-hutyl dimethyl silyl chloride produces the 6,1/6 -tri-O-silyl derivative in good yield (27). 

Sdylation of sucrose with 0.65 equivalents of ferZ-hutyl dimethyl silyl chloride in pyridine gives the corresponding 6 -, 6,6 -di-, and... 

The diisopropyl 2-dimethylphenylsilyl-2-propenyl- and 2-[cyclohexyloxy(dimethyl)silyl]-l,3,2-dioxaborolane-4,5-dicarboxylate reagents 7 and 8 were recently introduced for the enantiose-lective a- and y-hydroxyallylation of aldehydes86. 

Dimethylphenylsilyl-2-propenylboronate 7 is more enantioselective (81-87% ee with achiral aldehydes) than the 2-[cyclohexyloxy(dimethyl)silyl] compound 8 (64-72% ee), and consequently the former generally gives better results especially in mismatched double asymmetric reactions. Nevertheless, the examples show that appreciable double diastereoselection may be achieved with both reagents in many cases. 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

Diisopropylamino(dimethyl)silyl]-2-propenyl]lithium adds to aromatic and x-branched aldehydes in the presence of anhydrous zinc chloride with essentially complete anti stereoselectiv-ity3s. as expected from the chair-like pericyclic transition state formed by the ( -intermediate. The addition products are not isolated, but after O-silylation, oxidative desilylation with retention of configuration forms the rmft-diols. 

C ,H6 N204PS2Si 128778-86-9) see Tacrolimus [2S-[2a(R ),3p(5 )]]-3-[l-[[(l,l-dimethylethyl)dimethyl-silyl]oxy]ethyl]-a-methyl-4-oxo-2-azetidineacetic acid phe-nylmethyl ester... 

TSFPB tetrakis 4- [tcrt-butyl(dimethyl) silyl] -2,3,5,6-... 

Roush reported another tartrate boronate, (E )-y-[(menthofuryI)-dimethyl silyl]-allylboronate 130, for untz -a-hydroxyallyation of aldehydes. Reagent 130 can be obtained from commercially available menthofuran, which was selected... 

TSFPB tetrakis[4- tert-butyl(dimethyl)silyl -2,3,5,6-tetraliuorophenyl]borate... 

The enantiomerically pure l-[(benzyl(dimethyl)silyl)methyl]pyrrolidine, obtained from ben-zyl(chloro)(dimethyl)silane and (5,)-2-(methoxymethyl)pyrrolidine , afforded after deprotonation and subsequent alkylation the diastereomerically pure (by NMR spectroscopy) (a-alkylben-zyl)silanes2. To obtain this high degree of diastereoselectivity, the alkylation had to be performed in the weakly complexing solvent diethyl ether. In THF a diastereomeric ratio of only 3 1 was found with iodomethane as alkylating agent. 

Der Trialkylsilyl-Rest aus Trichloressigsaure-trialkylsilylestern wird mit Kaliumcarbonat unter Phasentransfer-Katalyse ebenfalls auf Imidazole iibertragen. Nach dieser Methode lassen sich z.B. 1-Trimethylsilyl-imidazol (80%) und l-(tert -Butyl-dimethyl-silyl)-imidazol (75%) herstel-len887. 

When electron-capture detectors are used, (bromoethyl)dimethyl-silyl ethers give a better response than the chloro derivatives.195... 

Bromobenzyl ferf-Butyl(dimethyl)silyl Ether (52) l24... 

Tetra-0-(terl.-butyl-dimethyl-silyl)- E14a/3, 645 f. (S-Ar - F)... 

Different protecting groups such as acetonides, /-butyl dimethyl silyl derivatives proved to be stable under these experimental conditions, but the benzylidene group is completely cleaved.. The rate of photodeoxygenation is greater at the secondary positions [82], as indicated in Scheme 43, with the regioselective photolysis of dipivaloate to give a mixture of monodeoxy and dideoxy derivatives (81) in low yields. 

A very simple preparation is the reaction of t-butyl-dimethyl-silyl chloride (508) with the substrate in presence of imidazole using DMF as solvent270 28 3 (Scheme 78). 

One of the key steps in the synthesis of the depsipeptide jasplakinolide involved the preparation of an aldehyde 273 by ozonolysis of an alkene 271 with the correct stereochemistry of the substituents (Scheme 83). The hydroxyl group was protected with R = fer7-butyl(dimethyl)silyl <2004ASC855>. 

Phosphorsaure-[(tert.-butyl-dimethyl-silyl)-methyl-amid]-dichlorid (54%) wire durch Oxygenierung des ent-sprcchcndcn Phosphorigsaure-amid-dichlorids mit Dimethylsulfo.xid in exothermer Reaktion erhalten239 ... 

The answer is to protect the hydroxyl group, and the group chosen here was a silyl ether. Such ethers are made by reacting the alcohol with a trialkylsilyl chloride (here f-butyl dimethyl silyl chloride, or TBDMSCl) in the presence of a weak base, usually imidazole, which also acts as a nucleophilic catalyst (Chapter 12). 

The reaction of a mesylate with indolylmagnesium iodide 566 gave indole 567, which was finally desilylated by careful treatment with aqueous HF to afford alcohol 568 with ee 70% (27% overall yield starting from 2-[/-butyl(dimethyl)silyl]oxy-l-phenyl-l-ethanol) (Scheme 115) <1996JOC984>. 

The cross-coupling reaction of alkenyl(fluoro)silanes with aryl halides sometimes produces, in addition to the desired ipso-cowpled products, small amounts of cmc-coupled products [14]. The czne-coupling is often striking in the reaction with organotin compounds. The isomer ratio of products produced by the reaction of l-fluoro(dimethyl)silyl-l-phenylethene with aryl iodides is found to depend on the electronic nature of a substituent on aryl iodides (Eq. 11) an electron-withdrawing group like trifluoromethyl and acetyl favors the formation of the ipso-coupled product. To explain the substituent effect, the mechanism depicted in Scheme 3 is proposed for the transmetalation of alkenylsilanes with palladium(ll) complexes. It is considered that an electron-donating substituent on Ar enhances... 

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