Silyl using

Tosylations, as well as silylations using trialkyl- or dialkyl-chlorosilanes in the presence of triethylamine, proceed with conservation of the three-membered ring (69DOK( l87)335). 

Another way to derivatize the OH group is by silylation using the Tri-sil Z reagent that will silylate the hydroxyl group, but not silylate the secondary amino group. 

These undergo silylation using the more reactive silyl triflate in the presence of 2,6-lutidine or triethylamine as base in dichloromethane. 

To prepare the corresponding cytosine containing nucleoamino acid 9, N -Boc cytosine was first silylated using N,0-bis(trimethylsilyl)acetamide (BSA) under carefully controlled conditions to produce mono-silylated-N -Boc cytosine 7. The mono-silylated product 7 undergoes l2-mediated nucleosidation with the O-MTM... 

The many derivatizing reagents commercially available include methanolic HC1 and diazomethane for methylation, and iV,(9-bis(trimethylsilyl)trifluoroacetamide (BSTFA), with or without 1% trimethylchlorosilane (TMCS), for silylation. Using BSTFA, hydroxyl moieties also can be silylated, giving the corresponding trimethylsilyl ethers. 

Silylation using the silylacetate (3.1.14) [49] involves the initial formation of the acetate carbanion, which abstracts a proton from the carbonyl compound or alcohol (Scheme 3.2, Table 3.5). When the reaction with a ketone is conducted in the presence of an aldehyde, crossed aldol products are obtained (see Chapter 6). 

N-Boc-4H-isoquinohne reacted quantitatively within 5 min with f-butyllithium in TMEDA to lead to the product silylated at the benzylic position.151 Another 4H-isoquinoline-type product has been silylated using lithium tetramethylpiperidide (LiTMP) in THF and the resulting compound has served as an intermediate in the synthesis of protoberberine.136,152 Interestingly, the intermediate lithium reagent did not react with the aldehyde group prior to silylation. A similar reaction has been done with the corresponding bromo derivative.153... 

The water-soluble fraction (from the original extraction of the reaction mixture described above) is evaporated to dryness, dissolved in 2 ml water, and applied to a Dowex AG 50 W x 8 column (H form, 200-400 mesh-column size, 0.6 x 5 cm). Water is used as the eluant, and the P-containing components are collected. The latter could be evaporated to dryness and silylated using the reagent pyridine/Tri-Sil TBT and BSTFA (1 2 2, v/v) (Pierce Chemical Co., Rockford, 1L). Subsequently an aliquot of this TMS derivative can be analyzed directly by the gas-liquid chromatography technique of Karlsson (1970). For further information on the detection and assay of choline and phosphocholine, suggested reading is an article by Kennedy (1991). 

A synthesis of Monocrotalic Acid was interrupted by problems with the 0 sily lation of a hemiacetal with low nudeophilirity [Scheme 4,68].114 Progress resumed when it was found that silver(I)-assisted silylation using terf-butyldi-methylsilyl chloride was efficient, giving a mixture of diastereoisomeric O-silyl acetals (dr = 2,7 1) in 93% yield. 

The surface modification was a two-step process including introduction of -SiCH=CH2 functions and their transformation to -SiCH2CH2SiCl. In the first step, the silica surface was subjected to silylation using a silicone coupling agent vinyltrichlorosilane, vinyltriethoxysilane, or... 

Off-line pyrolysis of a poly(4-vinylphenol) sample followed by the silylation using N,0-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) of the pyrolysate and GC/MS analysis with separation on a DB5 column (30 m length. 0.32 mm i d., 0.32 pm film thickness) is shown in Figure 6.6.2. The identification of the compounds in the silylated pyrolysate was done using MS library searches and is given in Table 6.6.3... 

Although, silylation using these conditions normally proceeds uneventfully, the following scheme shows that reactions are not always straightforward. ... 

Methallyl-TBDMS and Sc(OTf>3, CH3CH2CN, rt, 85-98% yield. Tertiary alcohols and phenols can he silylated using this method. The TES and TBDPS ether are also prepared hy this method. ... 

The following alcohol could not be silylated using conventional conditions. The use AgNOs made silylation possible. ... 

The preparation of silyl enol ethers has been reviewed. A nontraditional approach to their preparation involves a dehydrogenative silylation using a silane, a metal... 

The first approach to this problem was to attach the chiral auxiliary to the diene by a vinylogous trans-esterification reaction of chiral alcohols with the 3-alkoxy enones (Scheme 21). This reaction was used to construct a variety of chiral dienes including the menthol and phenmenthol dienes (55a) and (55b) by transesterification followed by enol silylation using the Simchen procedure (RsSiOTf taN). However, these dienes exhibit poor diastereofacial selectivity despite the precedent for high stereochemical control in homo Diels-Alder reactions by the use of similar auxiliaries on a,P-unsaturated enones. ... 

O-Silylation. Using [(coe)2RhCl]2 as catalyst ROH are silylated by vinylsilanes. ... 

The treatment of an ester (or lactone) with a base and a silyl halide or trillate gives rise to a particular type of sUyl enol ether normally referred to as a silyl ketene acetal. The extent of O- versus C-silylation depends on the structure of the ester and the reaction conditions. The less-bulky methyl or ethyl (or 5-tert-butyl) esters are normally good substrates for O-silylation using LDA as the base. Acyclic esters can give rise to two geometrical isomers of the silyl ketene acetal. Good control of the ratio of these isomers is often possible by careful choice of the conditions. The f-isomer is favoured with LDA in THF, whereas the Z-isomer is formed exclusively by using THF/HMPA (1.24). Methods to effect stereoselective silyl enol ether formation from acyclic ketones are less well documented. ... 

---