In the
presence of 1% of t-butyldimethylchlorosilane as the catalyst,
N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (BSMTFA)
functions as an extremely reactive t-butyldimethylsilylating
reagent for alcohols, amines, carboxylic acids, and thiols. Silylation
is generally completed within 5 min at 25°C in acetonitrile.
This amide is more reactive than N-(t-butyldimethylsilyl)-N-methylacetamide.
In the protection of a hydroxy group, the resultant tbutyldimethylsilyl
(TBDMS) ethers are stable under the conditions
for acetate saponification and hydrogenation.These silyl
ethers also remain intact towards the Jones reagent and Wittig
reagents. The TBDMS ethers are approx. 10 times more stable
against hydrolysis than the corresponding trimethylsilyl (TMS)
ethers.Selective removal of the TBDMS group can be accomplished
by use of dilute acetic acid or tetra-n-butylammonium
fluoride in THF at 25°C.
Silylation of ketones by use ofBSMTFAoccurs in triethylamine
and DMF at 40–60°C to give the corresponding silyl enol ethers
in good to excellent yields (eq 1).In addition, silyl ether formation
takes place in N-hydroxysuccinimide (88% yield) and Nhydroxypyrrole
(99% yield) by use of BSMTFA in THF.
