Indium-mediated β-allylation, β-propargylation, and β-allenylation onto α,β-unsaturated ketones: Reactions of in-situ-generated 3-tert-butyldimethylsilyloxyalk-2-enylsulfonium salts with in-situ-generated organoindium reagents

3-tert-Butyldimethylsilyloxyalk-2-enylsulfonium salts, generated in situ from the reaction of α,β-enones with dimethyl sulfide in the presence of TBSOTf, underwent a novel nucleophilic substitution with allylindiums to give silyl enol ethers of δ,ε-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 δ,ε-alkynyl ketones in good yields. Organoindium reagents derived from γ-substituted propargyl bromide and indium afforded the corresponding silyl enol ethers of β-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 ¹H NMR spectra.