Trimethylsilyl intermediates Trimethylsilylmethylation

Not surprisingly, two trimethylsilylmethyl groups further increase reactivity of cyclopropanes. Therefore 262 opens to 263 even at —78 °C yielding a new functionalized allylsilane as the product. An attempt to transform 262 into the corresponding P-ketosulfone 264 leads to the unusual cleaved compound 265, which carries an allyl and vinylsilane unit as well as the P-ketosulfone moiety. It is evident that this mode of cyclopropane opening is initiated under the basic reaction conditions by deprotonating the intermediate 264 in the side chain a to one of the trimethylsilyl groups 113). 

Intermediate 113 was transformed into the trimethylsilyl methyl ketone 119 in quantitative yield via the acid chloride, followed by the addition of trimethylsilylmethyl lithium (Scheme 2.13). Subsequent Peterson olefination of aldehyde 108 with 119 resulted in the required unsaturated ketone 120 in 95% yield. Subsequent desilylation and thioester hydrolysis afforded a 97% of the seco acid 121. Lactonization was achieved in 32% yield via the phosphoric acid-mixed anhydride, however this procedure also formed about 25% of the dimeric bis lactone. Following removal of the acetonide under the action of acid, a nonselective oxidation with RuCl2(Ph3P)3 produced a 1 1 mixture of the natural... 

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