Acetamide trimethylsilylating agent

Still another calixarene derivative of interest and utility is the trimethylsilyl ether. The hexa-trimethylsilyl ealix[6]arenes and octa-trimethylsilyl calix[8]arenes can be prepared 23) by using standard trimethylsilylating agents such as hexamethyldisilazene and chlorotrimethylsilane. The tetra-trimethylsilyl ethers of the calix[4]arenes, however, do not form under these conditions and require the use of the very reactive N,0-i (trimethylsilyl (acetamide 109). 

A new trimethylsilylating agent for alcohols, (46), is said to be more efficient than AO-bistrimethylsilyl acetamide. Quaternary ammonium alkoxides are the... 

Silylated pyrrohdone 388 reacts with formaldehyde to give 429 [41] whereas N-trimethylsilylsucdnimide 201 reacts with formaldehyde only in the presence of MesSiONa 96 at 100°C to give N-trimethylsilyloxymethylenesuccinimide ]42]. The silylating agent BSA 22a with formaldehyde at 75 °C gives the 0,N-acetal 430 [41]. Hydrated ninhydrin 431 is converted by N,0-bis-(trimethylsilyl)acetamide 22 a to the 0,N-acetal 432 ]43] (Scheme 5.12). 

BSTFA provided the highest yield of product in comparison to other silylating agents. BSA [bis(trimethylsilyl)acetamide] reacted with DDQ. TMSOTf with luti-dine or collidine in toluene offered the best alternative but the yield was lower than the yield achieved with BSTFA. 

Furoannelated analogs of uracil acyclic nucleosides were prepared as compounds with potential as anti-HIV agents (HIV = human immunodeficiency virus). Hence, 6-benzyluracil 320 is converted to the precursor 321 first by hydroxymethylation, silylation in situ with bis(trimethylsilyl)acetamide (BSA), then by alkylation (Scheme 28) <2001S559>. Ring closure to 322 was effected by treatment with lead tetraacetate and calcium carbonate <2004AP148>. 

N,0-bis(trimethylsilyl) acetamide mixed with HMDS and tri-methylsilyl amine have been suggested as a reagent for precolumn microreaction. An aqueous solution of the carbohydrate is injected into the microreactor followed by the silylating reagent mixture, and the products are automatically passed onto the column (83). Another silylating agent depicted in Equation 9.8,... 

It is possible to oxidize alcohols in the presence of free carboxylic acids.206 Nevertheless, sometimes better results are obtained if the acid is protected, for example by methylation.207 Sometimes, free carboxylic acids have a low solubility in cold CH2C12. In such cases, an in situ protection with the silylating agent, bis(trimethylsilyl)acetamide (BSA) normally allows the solubilization of the acid as trimethylsilyl ester, and an easy Swern oxidation. The resulting silylated acid is easily deprotected during the work-up.208... 

The decarboxylative Claisen rearrangement of allylic tosylacetate (5) and methyl tosylmalonate derivatives has been extensively studied. In the tosylacetate series, it has been found that acetate ions, base and a silylating agent, preferably N,0-bis(trimethylsilyl)acetamide (BSA), are all necessary, but in only catalytic quantities provided that BSA is used. Potassium acetate has been shown to be a suitable base. 

Lactams. Lactams, y-, 6, and e-, are obtained in high yield by treatment of amino acids with this silylating agent [or N,0-bis(trimethylsilyl)acetamide] at reflux for 4—48 hours. Work-up includes dilution with methanol or ethanol and evaporation. No racemization is observed. Trimethylsilyl esters are intermediates. Examples ... 

The Friedel-Crafts condensation is also useful for the synthesis of deoxynucleosides, e.g. 3 -azido-3 -deoxyadenosine. Recently, (3,(V-bis(trimethylsilyl)acetamide, instead of hexa-methyldisilazane (HMDS), has been used for the silylation. A, 7V-Bis(trimethylsilyl)acetamide does not introduce chemically interactive side products and has been found to be superior as a silylating agent, especially for one-pot reactions. ... 

Silylation with silyl chlorides or silyl triflates is performed in the presence of auxiliary bases, e.g. pyridine, TEA, imidazole, etc., in solvents such as CH2CI2, CHQ3, DMF, or As milder reagents A-methyl-G-(trimethylsilyl)acetamide and preferably A,C)-bis(trimethylsilyl)acetamide (BTMSA, 136) (Scheme 72) are used for such purposes. Since the acetamide that results from this reaction is difficult to remove from the reaction medium, cyanotrimethylsilanet or l-(trimethylsilyl)imidazole (137).t l may be used as alternatives. For quantitative silylation of amino acids containing additional side-chain functionalities, excess silylating agent is required. 

For the introduction of the TMS group under neutral conditions, trimethylsilyl chloride can be activated with lithium sulfide.Also trimethylsilylketene acetals (39), silyl enol ethers (40) (in particular those of pentane-2,4-dione), A -trimethylsilylacetamide (41), A, 0-bis(trimethylsilyl)acetamide (42), A A -bis(trimethylsilyl)urea (43) and A, 0-bis(trimethylsilyl)carbamate (44) are effective silylating agents under neutral conditions (Scheme 39). ... 

The C 0 bonds of ethers, acetals, and esters are cleaved with iodotrimethylsilane (eq (39)) [36]. Various halosilanes, silylamines, and N,0-bis(trimethylsilyl)acetamide are used not only for the protection of alcohols, amines, and carboxylic acids but also for the conversion of them to the volatilizable compounds for GC analysis (eq (40)) [37]. Silyltriflates act as silating agents as well as Lewis acids (eq (41)) [38]. 

Several silyl cyanides were prepared via the reaction of lithium cyanide with the appropriate chlorosilane. The lithium cyanide, which is both expensive and has a tendency to polymerize, was conveniently prepared by treatment of trimethylsilyl cyanide with w-butyllithium (equation 19). Using 2,6-di-rm-butylphenol as a test substrate, the authors found that although trimethylsilyl cyanide is less reactive than bistrimethylsilyl acetamide (BSA) as a silylating agent, it is more reactive than trimethylsilyl triflate26. 

Mass shifts in the spectra produced by different derivatizing agents may provide extremely useful information for the elucidation of certain structures. For example, the number of TMS groups attached to the parent compound can often be deduced by observing the mass shifts that occur upon replacing N,0-bis-(trimethylsilyl)-acetamide (BSA) with dg-BSA as the derivatizing agent. This information facilitates the identification of desoxymorphine-A,... 

A, 0-Z)M(trimethylsilyl)acetamide (BSA, a strong silylating agent) shifts this equilibrium towards the P(III) tautomer 22 These type of compounds are excellent ligands for Pd and Ir centres and have been used in challenging enantioselective allylic substitution reactions. ... 

Biotin is not volatile enough for direct GLC analysis but it is possible to use this technique after derivatizing the carboxylic group. Using bis-trimethylsilyl acetamide as silylating agent, Viswanathan et al. (117) described the quantitative determination of biotin after its conversion into its silyl ester. The column was a 2% OV 17 on diatomite (chromosorb G, AW/HMDS treated). n-Octosane was added as internal standard, and detection was achieved with a flame, ionization detector. The detection limit for biotin trimethylsilyl (TMS) ester was approxi-... 

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