Silyl enol ethers iodotrimethylsilane

Little quantities of iodotrimethylsilane catalyse the rearrangement of 2-siloxy cyclopropanes to their isomeric silyl enol ethers (equation 102), whereas an equimolar amount of this silylating agent gives a highly donor substituted diene. Both product types are promising intermediates, yet their chemistry still remains to be explored. 

Ring opening of oxiranes with iodotrimethylsilane provides silylated halohydrins <84CHEC-l(7)in). An exception to this reaction mode has been reported <9iJOC4598>. Silyl enol ether-terminated oxiranes, when treated with TMS-I in the presence of hexamethyldisilazide (HMDS) at low temperatures suffer C—C cleavage and cyclization to dihydrofurans. 

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. 

Few examples of intramolecular enol silyl ether or silyl ketene acetal cyclizations to oc,3-enones have been reported. Notable, as exemplified in Scheme 34, is the iodotrimethylsilane-mediated intramolecular cyclization of 5-(iodoacetoxy)-a,3-enones (211) to 5-lactones (214). These cyclizations proceed with in situ generated silyl ketene acetals (212) arising from iodotrimethylsilane reduction of the iodoacetoxy moiety.87... 

Enol silyl ethers (10, 97).2 Iodotrimethylsilane, generated in situ, is recommended for preparation of the enol silyl ether of acetone. The yield (60% based on chlorotrime-thylsilane) is comparable to that obtained using the more expensive trimethylsilyl triflate. 

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... 

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