Journal of the American Chemical Society 2003-08-13

Indium-mediated beta-allylation, beta-propargylation, and beta-allenylation onto alpha,beta-unsaturated ketones: reactions of in-situ-generated 3-tert-butyldimethylsilyloxyalk-2-enylsulfonium salts with in-situ-generated organoindium reagents.

Kooyeon Lee, Hyunseok Kim, Tomoya Miura, Koichi Kiyota, Hiroyuki Kusama, Sunggak Kim, Nobuharu Iwasawa, Phil Ho Lee

Index: J. Am. Chem. Soc. 125(32) , 9682-8, (2003)

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Abstract

3-tert-Butyldimethylsilyloxyalk-2-enylsulfonium salts, generated in situ from the reaction of alpha,beta-enones with dimethyl sulfide in the presence of TBSOTf, underwent a novel nucleophilic substitution with allylindiums to give silyl enol ethers of delta,epsilon-alkenyl ketones in good yields, which correspond to formal Michael addition products. In a similar manner, 1,4-propargylation of propargylindiums onto the sulfonium salts produced the corresponding silyl enol ethers of delta,epsilon-alkynyl ketones in good yields. Organoindium reagents derived from gamma-substituted propargyl bromide and indium afforded the corresponding silyl enol ethers of beta-allenyl ketones in good yields. The reaction proceeds via an addition-substitution mechanism involving the formation of allylic sulfonium salts. The presence of the intermediate sulfonium salt was confirmed by observation of the low-temperature (1)H NMR spectra.