Triflate triisopropylsilyl

Allyltriisopropylsilane, CH2=CHCH2Si(i-Pr)3 (1), b.p. 130716 mm. The silane is prepared by reaction of CH2=CHCH2MgBr with triisopropylsilyl triflate (96% yield). 

I I /0.0K mm. The reagent is prepared by reaction of 3-triisopropylsilyl-piopy nyllithium (this volume) with triisopropylsilyl triflate.1... 

This method provides a general route to trialkylsilyl triflates and has the advantage of circumventing use of the expensive silver triflate. Triisopropylsilyl triflate in combination with a base, preferably 2,6-lutidine, is effective for silylation of alcohols. 

Triisopropylsilyl ethers are formed under essentially the same conditions as TBS ethers — i.e. primary or unhindered secondary alcohols are treated with triisopropylsilyl chloride (bp 198 °C/98.5 kPa) in dichloromethane or DMF in the presence of imidazole or DMAP [Scheme 4.85J.138 The TIPS group is too bulky to react with a tertiary alcohol and protection of hindered secondary alcohols can be very slow in which case triisopropylsilyl triflate in the presence of 2,6-lutidine is used.100 However, even with the triflate as the silylating reagent, the reaction can be slow as illustrated by the reaction in Scheme 4.86.61 Triisopropylsilyl triflate is commercially available and it can be easily prepared on a large scale from triisopropylsilane and triflic acid in 97% yield. 

Simple organosilicon Lewis acids, for example trimethylsilyl triflate (la) [5], trimethylsilyl nonaflate (2) [6], iodotrimethylsilane [7], fert-butyldimethylsilyl triflate (Ic) [8], triisopropylsilyl triflate (Id) [8], etc., are commercially available, but because of their easy hydrolysis and the appearance of traces of a protic acid during storage. 

A fourth type of product, a carbamate RNHCOOR , can be obtained from primary or secondary amines, if these are treated with CO, O2, and an alcohol R OH in the presence of a catalyst. " Primary amines react with dimethyl carbonate in supercritical CO2 (see p. 414) to give a carbamate. " Carbamates can also be obtained from nitroso compounds, by treatment with CO, R OH, Pd(OAc)2, and Cu(OAc)2, " and from nitro compounds. " When allylic amines (R2C=CHRCHRNR 2) are treated with CO and a palladium-phosphine catalyst, the CO inserts to produce the p,y-unsa-turated amides (R2C=CHRCHRCONR 2) in good yields. " Ring-expanded lactams are obtained from cyclic amines via a similar reaction (see also, 16-22). Silyloxy carbamates (RNHC02SiR 3) can be prepared by the reaction of a primary amine with carbon dioxide and triethylamine, followed by reaction with triisopropylsilyl triflate and tetrabutylammonium fluoride. ... 

The TIPS group is usually introduced from triisopropylchlorosilane [336], but protection of hindered alcohols can be very slow in which case triisopropylsilyl triflate in the presence of 2,6-lutidine is used [293]. 

Diazomethane is explosive [1] In contrast, no explosions or toxicity have been noted with the silyldiazomethane derivatives [(R3SiC(N2)H 1, R=Me [2] 2, R=/Pr [3]), which can be purified by distillation (1, 75°C/760 mm Hg 2, 39°C/10" mm Hg). Compound 1 is commercially available, while 2 is easily prepared in 45 % isolated yield by the sequential addition of an ethereal solution of diazomethane followed by triisopropylsilyl triflate at -20°C to neat diisopropylethylamine [3]. 

Trifluoromethanesulfonic acid (0.226 mol) is added dropwise to triisopropylsilane (0.242 mol), stirred under an inert atmosphere and cooled to 0 °C in a flask fitted with dropping funnel, gas inlet, exit tubes and thermometer. After the addition is completed, stirring is continued at 22 °C for 16 h. Triisopropylsilyl triflate (97%) is isolated by the distillation through a 30 cm vacuum jacketed Vigreux column. 

The pyran indicated, 2,3-dihydro-2,2-dimethyl-6-phenyl-4H-pyran-4-one and benzoylacetylene in chloroform containing 2.5 moles of 2,6-di-tert-butylpyridine unden/vent additton in the presence of excess triisopropylsilyl triflate by stirring... 

C2 silylation as a protecting group strategy for oxazoles has historically been difficult due to the preferential oxophilicity of standard silyl chlorides protection of the ring opened oxygen atom typically predominates rather than protection of the C2 carbon atom. Miller has shown that treatment of imsubstituted oxazole with -BuLi followed by triisopropylsilyl triflate yields C2-silylated oxazole in near quantitative yield. Furthermore, this protected oxazole is stable to nonacidic aqueous workup and... 

Triisopropylsilyloxy) acrolein, which could be prepared by a concise reaction of triisopropylsilyl triflate (TIPSOTf) and 2-methoxy-2-methyl-[l,3]dioxan-5-one in the presence of triethylamine (TEA), reacted with selected dienes in the presence of a catalytic amount of Sc(OTf)3 to give the products that were formally [4 + 3] cycloadducts (Scheme 12.19) [35]. In the case of butadiene, only a [4 + 2] cycloadduct was observed. 

---