Indium-Mediated β-Allylation, β-Propagylation, and β-Allenylation onto α,β- Unsaturated Ketones: Reaction of in-Situ-Generated 3-t-Butyldimethyl-sily

Abstract

3-tert-Butyldimethylsilyloxyalk-2-enyisulfonium 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 H-1 NMR spectra.