Activations iodotrimethylsilane

The acetal 14, activated by the iodotrimethylsilane 17, produces the oxonium cation 16 which can be intercepted by allylsilane 1 yielding homoallylic ether 15, one equivalent of methoxytrimethylsilane 18 and the catalyst 17. 

Deoxygenation of aieohols and ethers. Treatment of alcohols and methyl or trimethylsilyl ethers in acetonitrile with this iodotrimethylsilane equivalent and then zinc (previously activated with aqueous hydrochloric acid) and a little acetic acid results in deoxygenation to alkanes, usually in 60-90% yield. Presumably an alkyl iodide is an intermediate. 

With an acceptor-substituted alkene moiety tethered to the molecule, the intermediate silyl enol ether may undergo an intramolecular [2-I-2] cycloaddition.The silyl-assisted addition of hydrogen halides to cyclopropanes is not restricted to ketones with carbonyl groups as activating function or iodide as nucleophile. Esters and other acid derivatives underwent similar reactions when treated with iodotrimethylsilane alone or in the presence of an additional catalyst such as mercury(II) or zinc(II) chloride.Subsequent treatment of the y-iodo ester with potassium carbonate in tetrahydrofuran gave the respective y-butyrolactones in good yield. 

Optically active thiazolidine -oxides (259) undergo the silicon Pummerer reaction with t-butyldimethylsilyl trifluoromethanesulfonate or iodotrimethylsilane <87TL5903>. When the former is used as silylating agent, thiazolidines (260) and 4-thiazolines (261) are obtained. With iodotrimethylsilane, the iodothiazolidines (262) and the dihydro-1,4-thiazine (263) are obtained (Scheme 65). 

Notes and discussion. Methyl a-D-gluco- and mannopyranosides and a-D-glycopyranosyl chlorides can react with allylsilanes via activation with trimethylsi-lyl trifluoromethanesulfonate or iodotrimethylsilane to stereoselectively afford the corresponding a-C-allylated glycopyranosides in excellent yields. The yields of the reactions depend on the solvent and the amount of catalyst employed. Acetonitrile is the most suitable solvent whereas dichloromethane, the most commonly used solvent for allylation reactions using allylsilanes, does not afford satisfactory results. The reactions proceed very slowly when promoted by less than 5 mol% of the catalyst, however, the use of 50 mol% of catalyst is sufficient to force the reactions to completion. 

The Morita-Baylis-Hillman reaction of imines with ynones in the presence of iodotrimethylsilane was efficiently catalyzed by ZrCU (Equation 15) [20]. Compared with the other Lewis acids, ZrCU showed much higher activity for the reaction. The newly formed olefin moiety has (E) configuration exclusively. 

SUylation with HMDS is most commonly carried out with acid catalysis. The addition of substoichiometric amounts of chlorotrimethylsilane (TMSCl) to the reaction mixtures has been found to be a convenient method for catalysis of the silylation reaction. The catalyticaUy active species is presumed to be hydrogen chloride, which is liberated upon reaction of the chlorosi-lane with the substrate. Alternatively, protic salts such as ammonium sulfate can be employed as the catalyst. Addition of cat-al)Tic lithium iodide in combination with TMSCl leads to even greater reaction rates. Anilines can be monosilylated by heating with excess HMDS (3 equiv) and catalytic TMSCl and catalytic Lil (eq 2). Silylation occurs without added Lil however, the reaction is much faster in the presence of iodide, presumably due to the in situ formation of a catalytic amount of the more reactive iodotrimethylsilane. 

General Discussion. 2,4-Pentadienyltrimethylsilane is used as a stable (storable) nucleophilic substitute for pentadienyllithium. This compound reacts with Lewis acid (boron trifluoride etherate, iodotrimethylsilane, titanium(IV) chloride) activated electrophiles in the same manner as allylsilanes (eq 1). Generally only e-substitution is observed (cf. Table 1). ... 

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