Additions iodotrimethylsilane

The selective and facile cleavage of the benzylic ether linkages of 1,2,3 or 4 is accomplished by treatment with iodotrimethylsilane to form the corresponding benzylic iodide. Further addition to these iodide derivatives of 1 affords dendrimers of generation 1 with phosphonium ion sites at the periphery. Such a strategy is conducted up to generation 3 with a phosphine or a phosphonium core (Scheme 3). 

In the presence of proton and/or Lewis acids and strong nucleophiles bicyclo[4.2.0]octan-7-ones were converted to 3-substituted cyclooctanones (see table overleaf). 3-Iodocyclooctanones were formed on treatment with iodotrimethylsilane and catalytic amounts of zinc(II) iodide.31 If l,8-diazabicyclo[5.4.0]undecene was added after the rearrangement a cyclooctenone33 was isolated. Similarly, benzenethiol underwent addition to the central bond of bicyclo[4.2.0]octan-6-ones in the presence of zinc(ll) chloride and hydrochloric acid under anhydrous conditions to form 3-(phenylsulfanyl)cyclooctanones.34... 

Acetaliziation and aUylation of carbonyl compounds Iodotrimethylsilane is an effective catalyst for acetalization with an alkoxysilane. Addition of allyltrimethylsilane to this reaction results in allylation of the acetal to form a homoallyl ether. 

Conjugate addition to enones. Iodotrimethylsilane can mediate conjugate addition of furanes to a,p-enones via the intermediate y-iodo enol silyl ether (9, 252-253). The adduct can be isolated as the enol silyl ether or the corresponding ketone (equation I).6... 

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. 

Acid-catalysed addition of primary, secondary, and tertiary alcohols to 3,4-dihy-dro-2//-pyran in dichloromethane at room temperature is the only general method currently in use for preparing THP ethers and the variations cited below concern the choice of acid. The reaction proceeds by protonation of the enol ether carbon to generate a highly electrophilic oxonium ion which is then attacked by the alcohol. Yields are generally good. Favoured acid catalysts include p-toluenesulfonic acid or camphorsulfonic acid. To protect tertiary allylic alcohols and sensitive functional groups such as epoxides, the milder acid pyridinium p-toluenesulfonate has been employed (Scheme 4.316]. A variety of other acid catalysts have been used such as phosphorus oxychloride, iodotrimethylsilane- and bis(trimethylsilyl)sulfate. but one cannot help but suspect that in all of these cases, the real catalyst is a proton derived from reaction of the putative catalysts with adventitious water. Scheme 4.317 illustrates the use of bis(trimethylsilyl)sulfate in circumstances where other traditional methods failed. - For the protection of tertiary benzylic alcohols, a transition metal catalyst, [Ru(MeCN)2(triphos)](OTf)2 (0.05 mol%) in dichloromethane at room temperature is effective. ... 

Although mechanistically different, functionalized alkenylsilanes are prepared stereoselectively by the reaction of 1-alkynes with iodotrimethylsilane (123) and diethylzinc. At hrst oxidative addition of 123 to Pd(0) generates 125. Then insertion of 1-octyne to 125 affords the alkenylpalladium 126. Transmetallation with Et2Zn gives 127 and reductive elimination provides the alkenylsilane 124. The reaction can be regarded as a Heck-type reaction of alkyne with MesSi-I, followed by Negishi coupling [37]. 

Cleavage of the ketene 0,5-acetals under neutral or mildly basic conditions can be executed by using iodotrimethylsilane to give the phenyl thioester or the ketene 0-silyl,5-acetal (eqs 3 and 4). In addition, amides can be prepared by sequential treatment of ketene 0,5-acetals with lithium thiomethoxide in HMPA followed by addition of an amine (eq 5). ... 

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. 

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