Epoxides iodotrimethylsilane

EPOXIDES Alumina. r-Butyldimethyl-iodosilane. n-Butyllithium-Magnesium bromide. Cyclohexylisopropylamino-magnesium bromide. Dialkylaluminum amides. Iodotrimethylsilane. Lithium l-r ,< -dimethyldibenzylamide. Nafion-H. Organoaluminum compounds. Pyri-dinium chloride. Raney nickel. Tri-fluoroacetyl chloride. Trimethylsilyl-acetonitrile. Tris(phenylseleno)borane. Zinc iodide. 

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. ... 

In Situ Generation of Iodotrimethylsilane. Of the published methods used to form TMSI in situ, the most convenient involves the use of TMSCl with Nal in acetonitrile. This method has been used for a variety of synthetic transformations, including cleavage of phosphonate esters (eq 23), conversion of vicinal diols to alkenes (eq 24), and reductive removal of epoxides (eq 25). ... 

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