Diisopropylsilyl bis(trifluoromethanesulfonate)

bp 85–86°C/2mmHg;d 1.396 g cm3; fp 110°C.

Diisopropylsilyl bis(trifluoromethanesulfonate) has more recently been used to prepare diisopropylsilyl-linked oligonucleotide analogs. Silylation of 5'-O-(dimethoxytrityl)-2'-deoxynucleosides using diisopropylsilyl bis(trifluoromethanesulfonate) and the hindered base 2,6-di-t-butyl-4-methylpyridine (Dtbp) provided quantitative yield of 3'-O-diisopropylsilanols (eq 2). Hence, silylation of 5'-O-(dimethoxytrityl)thymidine, N6-benzoyl-2'-deoxy-5'-O- (dimethoxytrityl)adenosine, N4-benzoyl-2'-deoxy-5'-O-(dimethoxytrityl) cytidine, and N2-isobutyryl-2'-deoxy-5'-O-(dimethoxytrityl) guanosine gave the desired products 5a–d in excellent yields.
Coupling of products 5a–d with unprotected thymidine resulted in formation of 3',5'-linked dinucleosides 6a–d selectively, and the dimer 7 from reaction with secondary hydroxyl group of thymidine was not observed (eq 3). Subsequent silylation and coupling with another molecule of thymidine gave 3,5- linked trinucleoside 8 in 76% yield (eq 4). A tetrathymidylate oligomer was prepared by 3'-O-silylation of 8 followed by coupling with thymidine. Although no self-condensation was observed, only 30% of the product 9 was obtained after purification by preparative HPLC.

conveniently prepared by the slow addition of 2 equiv of trifluoromethanesulfonic acid to a stirring mixture of chlorodiisopropylsilane, followed by direct distillation of the product from the reaction flask to yield the product as a pale yellow oil.

DIISOPROPYLSILYL BIS(TRIFLUOROMETHANESULFONATE) should be stored in the refrigerator under an inert atmosphere of argon or nitrogen. Special care should be used when handling since diisopropysilyl bis(trifluoromethanesulfonate) has been classified as a corrosive.