Silylations trimethyl trifluoromethanesulfonate

Even greater diastereoselectivity is achieved by performing the cyclization with silylated malate 12 at —25 °C in the presence of 9 mol% trimethyl trifluoromethanesulfonate. Di-oxolanone 170 is obtained with a cis. trans ratio 100 1 [21]. The stereoselectivity in this reaction is highly temperature dependent. Raising the reaction temperature to 0 °C drastically reduces the cis trans ratio (to 4 1). 

Table 1 summarizes the results of the reactions of ynoates (2a-c) with a silicon enolate (silyl ketene acetal) and a lithium enolate of methyl propionate (Eq. 1). Except for the reaction of 2c, Fe-Mont catalyzed exclusive 1,2-addition of silyl ketene acetal to 2a and 2b to give an adduct of 3 in high yields. However, even trimethyl silyl trifluoromethanesulfonate (TMSOTf), a generally applied homogeneous strong acid, failed to effect the addition reaction. 

Several different methods have been employed for the preparation of diazo(trimethylsilyl)meth-ane (1). At present, the best synthetic method seems to be the diazo transfer reaction between diphenylphosphoryl azide and (trimethylsilyl)methylmagnesium chloride.However, the product often contains (chloromethyl)trimethylsilane and hexamethyldisiloxane as impurities. This method can also be employed for the synthesis of diazo(triethylsilyl)methane and diazo(di-ethylmethylsilyl)methane. The diazo transfer reaction can also be carried out with (trimethyl-silyl)methyllithium and tosyl azide. Other methods are the silylation of diazomethane with (trimethylsilyl)trifluoromethanesulfonate or chloro(trimethyl)silane and the base-induced cleavage of A-nitroso-A-[(trimethylsilyl)methyl]urea or the related carbamate or acet-amide.2° =... 

TL7475], in the presence of boron trifluoride diethyl etherate or trimethyl-silyl trifluoromethanesulfonate gives the corresponding 2-oxoalkyl-, 3-oxo-alkyl-, alkoxycarbonylmethyl- and allyltriarylbismuthonium salts, respectively. 

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