Silylating reagents reactivities

Several methods for the preparation of the parent compound in this system, tris(trimethylsilyl)phosphite, have been reported.114 118 The application of this and related reagents in reaction with alkyl halides has been reported and used for the preparation of a variety of phosphonic acid analogues of phospholipids.114119-124 Interestingly, alkyl chlorides appear to be more reactive with the silyl reagents than do alkyl iodides, a reversal of the normally observed trend with alkyl esters of the phosphorus acids. (The particular use of silyl phosphorus reagents for the synthesis of biologically significant compounds has... 

Sllylation. This triflatc is a very reactive silylating reagent. It was used successfully to prepare l,4-bis(i-butyldimethylsilyloxy)-2,5-di-r-butylbenzcnc (88% yield). 

The steric demand ol the /e/7-butyl group in TBSC1 reduces the reactivity of this silylating reagent to such an extent that not only the base imidazole but also the dipolar aprotie solvent DMF must be added. Moreover, primary alcohols react more rapidly than secondary alcohols, while tertiary alcohols are inert under these conditions.16 It is therefore possible to distinguish between the two free hydroxy functions in diol 25. 

In the first step the cyclic acetal is subjected to acid cleavage, after which all the free alcohol functions are protected as TBS ethers with the aid of the very reactive silylation reagent I BS triflate. The primary alcohol is then deprotected under mild conditions and oxi-di/ed with FDC to a carboxylic acid. 

The most reactive of the silylating reagents is used for TBS-pro-tection of the alcohol. 

Step 2 Protection of the sterically hindered 2° alcohol requires the use of the reactive silylating reagent TBSOTf. 

The TBDMSC1 reacts with imidazole to give the intermediate depicted in Figure Si2.3. In its protonated form the intermediate is a highly reactive silylating reagent. 

This difference in chemical reactivity can be converted into a differential etch rate by treating the exposed film with an appropriate silylating reagent. For example, chlorotrimethylsilane, hexamethyldisilazane and bis(trimethylsilyl)acetamide are well know to react with phenolic hydroxyls, carboxylic acids and other nucleophilic species to form the corresponding trimethylsilyl derivatives. 

In this scheme, a functionality that does not react with a silylating reagent is converted to a reactive group to incorporate Si selectively in the exposed area, or conversely, a reactive functionality is rendered inert by a radiation-induced process so that Si is selectively introduced in the unexposed region. 

Formation of Silyl Enol Ethers. TMS-I in combination with Triethylamine is a reactive silylating reagent for the formation of silyl enol ethers from ketones (eq 22). TMS-I with Hexam-ethyldisilazane has also been used as an effective silylation agent, affording the thermodynamic silyl enol ethers. For example, 2-methylcyclohexanone gives a 90 10 mixture in favor of the tetra-substituted enol ether product. The reaction of TMS-I with... 

Reaction with Amines. Reaction of Tf20 with hexam-ethyldisilazane affords the reactive silylating reagent N,N-bis(trimethylsilyl)trifluoromethylsulfonamide. This compound exists in two tautomeric forms in solution, related by trimethylsilyl shifts between oxygen and nitrogen (eq 50). ... 

HMIS Health 3, Flammability 3, Reactivity 1 Uses Electrophilic reagent silylation reagent Manuf./Distrib. AP Resources http //www.apr.co.kr. Advanced Synthesis Tech. http //www. advancedsynthesis. com, Aldrich http //www.sigma-aidrich.com, Fluka http //www.sigma-aidrich. com, Gelest http //www.geiest. com Sigma... 

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