R-Butyldimethylsilyl triflate

Asymmetric intramolecular double Michael reaction.3 Treatment of the 8-phenylmenthyl ot,(3-unsaturated amide ester (2) with r-butyldimethylsilyl triflate and triethylamine effects this Michael reaction with almost complete diastereose-lectivity to give the indolizidine 3, which was used for synthesis of (- )tylophorine (4). 

The treatment of glutarimide (586) with two equivalents of r-butyldimethylsilyl triflate (587) in the presence of Et3N gives rise to 2,6-bis(t-butyldimethylsiloxy)-3,4-dihydropyridine (588) (equation 297)330. Quinone (589) and hexamethyldisilazane (405) in the presence of iodine as catalyst form l,4-bis(TMS)-hydroquinone (590) (equation 298)331. 

Silylation at nitrogen with r-butyldimethylsilyl triflate, generates pyridinium salts which, because of the size of the N-substitutent, react with Grignard reagents exclusively at C-4 montmorillonite-catalysed addition of silyl enol ethers to pyridines has a comparable effect in producing l-trimethylsilyl-1,4-dihydropyridines carrying an acylalkyl substituent at C-4. ... 

This triflate has been prepared by reaction of r-butyldimethylsilyl chloride with silver triflate (expensive)1 or triflic acid (80% yield).2 Since this triflate is sensitive to moisture, it should be used soon after preparation. In combination with 2,6-lutidine, it converts even tertiary alcohols into r-butyldimethylsilyl ethers in 70-90% yield. 

The conversion of epoxides to allylic alcohols (Scheme 24) can also be considered here. A variety of reagents, including lithium diethylamide, r-butyldimethylsilyl iodide, a dialkylboryl triflate and an ethylaluminum dialkylamide have been used successfully. 

Although alkylation of 3-hydFoxy ester dianions occurs with high diastereofacial selectivity, the aldol reaction of the dianion obtained from methyl 3-hydroxybutanoate with benzaldehyde gives all four dia-stereomeric aldols in a ratio of 43 34 14 9 (equation 117). On the other hand, dianions of 8-hydroxy esters show rather good diastereofacial preferences under the proper conditions. Deprotonation of t-butyl-5-hydroxyhexanoate with lithium diethylamide in the presence of lithium triflate gives an enolate that reacts with benzaldehyde to give aldols (196) and (197) in a ratio of 91 9 (equation 118). Use of the r-butyldimethylsilyl ether instead of the alcohol resulted in no facial preference. 

Di-f-butylmethylsilyl trifluoromethanesulfonate, r-Bu2MeSiOTf. The triflate is obtained as an oil, b.p. 63-65°/15 mm, by reaction of f-Bu2MeSiH with triflic acid (95% yield). The reagent is used to prepare DTBMS esters and ethers, which are more stable than the t-butyldimethylsilyl counterparts. Thus the esters are not reduced by lithium t-butyldiisobutylaluminum hydride (10, 239-240) or hydrolyzed by acid, but are cleaved by BU4NF.1... 

Alkylations are Friedel-Crafts-type electrophilic reactions requiring the participation of a strong Lewis catalyst. Obviously they were carried out in the presence of hazardous Lewis acid catalysts as metal halides. Switching from these molecular compounds to solid embedded triflates led to catalysts on which such reactions occurred with turnover frequency (TOFs) having at least one order of magnitude higher than on classic acid solid catalysts as zeolites [100,101]. Examples of such reactions are alkylations of phenols or naphthols occurring on immobilized La, Ag, or r rr-butyldimethylsilyl-trifluoromethane-sulfonate catalysts. 

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