Introduction
Di-tert-butylsilyl bis(trifluoromethanesulfonate) is a useful reagent in organic synthesis. It is a colorless to yellow or light brown-yellow liquid with a boiling point of 73–75 °C, it is sensitive towards moisture, corrosive and reacts with hydroxylic solvents. It has been prepared by reaction of di-tert-butylchlorosilane with trifluoromethanesulfonic acid[1] but it is also commercially available. It has been applied in intramolecular cyclizations as a novel promoter for a Boekelheide reaction.[2] It acts as protecting group for 1,3-diols to improve yield and stereoselectivity of organic reactions,[3] for 1,2-diols in a synthesis of dienophiles[4] and 1,4-diols to obtain 3,6-bridged glycosyl donors[5] and to receive natural products.[6] Triethylsilyl ether, isopropylidene ketal would perform the same role as the t-Bu2Si(OTf)2; however, their acidic removal could be problematic in some cases.[7] The bridging di-tert-butylsilylene can be cleaved to give the corresponding fullerene polyols.[8] Moreover, this reagent is a valuable material for the synthesis of prodrugs of chemotherapeutics.[9]
Table 1Use of Di-tert-butylsilyl Bis(trifluoromethanesulfonate)
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(A) Massaro and co-workers have treated (aminoalkyl)quinoline N-oxide 1 with t-Bu2Si(OTf)2 and triethylamine in dichloromethane to obtain 2-(N-benzylpyrrolidin-2-yl)quinoline 2 by intramolecular Boekelheide reaction.[2] The cyclized product 2 was synthesized in 51% yield, which was increased to 75% by using microwave irradiation.
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(B) Di-tert-butylsilyl bis(trifluoromethanesulfonate) is reported to be a useful reagent for the preparation of C3−5-O-silylated 2-deoxythioriboside 4. This product was formed from the corresponding thioglycoside 3 in the presence of 2,6-lutidine in good yield (83%). The C3−5-O-silylated group of compound 4 influences the stereoselectivity during its glycosylation.[3]
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(C) The electron-rich dienophile 7 was obtained starting from the commercially available peracetyl fucal 5.[4] Compound 5 was first deprotected and then the hydroxyl groups at C-3 and C-4 of 6 were protected by reaction with di-tert-butylsilyl bis(trifluoromethanesulfonate) under mild conditions. Fucal derivative 7 was used in a highly selective Diels–Alder reaction.
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(D) The reaction of 2,4-di-O-benzyl-1-thio derivatives of glucose, mannose and galactose 8–10 with di-tert-butylsilyl bis(trifluormethanesulfonate) in 2,6-lutidine led to 3,6-bridged glycosyl donors 11–16 in moderate yields.[5] A number of other bridging reagents were examined but no products were observed.
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(E) The reaction of substituted dibenzofuran with di-tert-butylsilyl bis(trifluoromethanesulfonate) in the presence of a base such as pyridine has given the derivative of dibenzofuran 18. The reaction was applied to obtain aglycone fulicinerine.[6]
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(F) Treating compounds 19a–b (2 equiv) with t-Bu2Si(OTf)2 (1 equiv), Guerra and co- workers have afforded the corresponding bis-malonates 20a–b, which they then used for the regioselective bis-functionalization of C60.[8]
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(G) Asymmetric bifunctional silyl ether (ABS) prodrugs of chemotherapeutics (camptothecin, dasatinib, and gemcitabine) were obtained in one step by reacting a dichlorodialkyl silane (i-Pr, Et,) or t-Bu2Si(OTf)2 with the pendant alcohol on the chemotherapeutic.[9] This kind of combination of a silyl ether, a chemotherapeutic and a polymerizable monomer ensures protection for the drugs and decreases the rate of degradation.
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