Silyl-Based Reagents TMSOTf

Two closely related methods for the direct transformation of THP ethers into TBDMS ethers, using TBDMSOTf and a tertiary amine base, have been disclosed72,73. This reagent system has been reported74 to perform the same transformation on t-butyl and t-amyl ethers. In a similar vein75, p-methoxybenzyl ethers are converted directly into the corresponding silyl ethers using TMSOTf and triethylamine. 

Reagents i, EtaN, Mo(CO)s ii, MeCOaH iii, AC2O. py iv, silylated base, TmsOTf V, NaOMe, MeOH... 

Reagents i, silylated base, TMSOTf, (CH2C1)2 Scheme 1... 

Trimethylsilylation has been accomplished with a large number of reagents most of which are commercially available. The cheapest (chlorotrimethylsilane) and the most reactive (trimethylsilyl triflate) rapidly silylate hydroxyl groups in the presence of a suitable base such as pyridine, triethylamine, i-Pr2NEt, imidazole, or DBU but an aqueous workup is required to ensure complete removal of the resultant amine hydrochloride or triflate whence hydrolysis of the nascent TMS ether may occur. In some cases the insoluble salt may be removed by filtration without aqueous workup. A wide range of solvents can be used for the reaction such as dichloromethane, acetonitrile, THF, or DMF. Care must be taken with trimethylsilyl triflate (TMSOTf) since it will convert aldehydes and ketones to the corresponding enol silanes and it will open epoxides in a reaction that has preparative significance [Scheme 4.6]. Similar transformations can be accomplished with tert-butyldimelhylsilyl triflate (TBSOTf) or triethylsilyl triflate (TESOTf). ... 

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