Reactions of pentafluorophenyltrimethylsilane and cyanomethyltrimethylsilane with carbonyl compounds catalyzed by cyanide anions

Treatment of pentafluorophenyltrimethylsilane (I) and cyanomethyltrimethylsilane (II) with enolizable ketones in the presence of a catalytic amount of potassium cyanide-18-crown-6 complex gave the corresponding trimethylsilyl enol ethers. The same dehydrogenative silylation of acetylacetone and benzoylacetone with silane I was extended to the preparation of 2,4-bis(trimethylsiloxy)-1,3-pentadiene and 1-phenyl-1,3 -bis(trimethylsiloxy)-1,3-butadiene, respectively. The dehydrogenative silylation of acetylacetone and benzoylacetone with dimethylbis(pentafluorophenyl)silane under the same conditions affords novel heterocyles 5-methylene-2,6-dioxa-1-silacylohex-3-enes. In the reaction studied the silylating ability of the silanes increases in the order Me₃SiCN ? Me₂Si(CN)₂ < Me₃SiCH₂CN < Me₃SiC₆F₅ ? Me₂Si(C₆F₅)₂. On the other hand, potassium cyanide-18-crown-6 complex catalyzed the addition of silane I or II to a carbonyl group of non-enolizable compounds such as benzaldehyde, crotonaldehyde, and methyl(triethylgermyl)ketene.