Power Chemical Corporation - SiSiB® SILANES (Full Catalogue, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10)

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SiSiB® Silane Blocking Agents


Silyl groups have long been employed to derivatize and protect various substrates during chemical and synthetic sequences. Initial work involved derivatizing compounds by replacing active hydrogen at-oms with silyl groups. These classic silylation reactions have not changed appreciably over the last de-cade. The early utilization of silylation was in the area of analysis. The more volatile silyl derivatives of alcohols, carboxylic acids, phenols, amino acids, carbohydrates and amines could be analyzed through their retention times by gas chromatography. Later it was noted that silylation had great synthetic poten-tial. Replacement of active hydrogens with silyl groups afforded products which were more chemically stable and would undergo subsequent chemical reactions at sites other than the silyl blocked one. Hydrolysis would then regenerate the unprotected functionality. A major factor contributing to the wide acceptance of silyl blocking groups is that both blocking and de-blocking reactions are high yield reactions and often quantitative. This has led to the introduction of a wide range of specialty blocking agents which have been designed for specific purposes such as selectivity, degree of reactivity for less reactive sub-strates, nature of silylation by product for sensitive substrates, and stability of the blocked substrate to-wards other reagents. Some of the more prominent silylating agents are discussed individually below.

t-Butyldimethylchlorosilane (PC5710)

Because of the steric bulk of the t-butyldimethylsilyl group, it is relatively stable against de-block-ing in weakly acidic or basic media and mild oxidizing and reducing conditions. It is unaffected by hydrogenolysis over palladium and lithium aluminum hydride. Substrates blocked by the t-butyldimethylsilyl group are also stable against Grignard reagents. The stability of this blocking group has been a major factor in developing syntheses of prostaglandins, and it has found extensive use in terpenoid and carbohy-drate chemistry. In addition to the foregoing, PC5710 has been utilized in the protection of alcohols, amines, carboxylic acids, phenols and other substrates. Preparation of blocked intermediates is most satisfactorily achieved by reaction of the substrate with PC9003 in the presence of a molar excess of imidazole using DMF as solvent. Removal of the t-butyldimethylsilyl group is readily accomplished through hydrolysis using acetic acid, acetic anhydride containing FeCI3 or with tetrabutylammonium fluoride in THF.


This reagent provides blocked derivatives having even greater stability than can be achieved employing PC5710. This blocking agent is utilized where the highest stability is desired. Hydroxyl derivatives prepared utilizing PC8710 are stable to 80% acetic acid (which cleaves t-butyldimethylsilyl derivatives), 50% aqueous trifluoroacetic aciddioxane, hydrogenation over Pd, Grignard reagents and lithium alumi-num hydride. Blocked derivatives are very resistant to hydrolysis and oxidation. Derivatization is effi-ciently carried out using a molar excess of imidazole in DMF solvent. Hydrolysis is effected with tetrabutylammonium fluoride in THF.

Triisopropylchlorosilane (PC5950)

This material has found new applications as a blocking group. It has been utilized to prepare blocked derivatives of hydroxy compounds. Derivatization of substrates is accomplished efficiently in DMF containing a slight molar excess of imidazole. Blocked intermediates exhibited acidic hydrolytic stability intermediate between that of a PC5710 and PC8710 derivatives. Greater stability was obtained with PC5950 under basic conditions. With n-butyl alcohol as the substrate, the following half-life stabilities were recorded.

Blocking Reagent H OH
PC5710 <1min 1h
PC5950 18min 14h
PC8710 244min <14h

Deblocking is achieved by reaction with tetrabutylammonium fluoride in THF.

Full Catalogue, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10 Sales Centre


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