Iodotrimethylsilane-Promoted 1,4-Addition of Copper Acetylides to α,β-Unsaturated Ketones and Aldehydes

In the presence of iodotrimethylsilane (TMSI) and lithium iodide in tetrahydrofuran, the otherwise unreactive copper acetylides add to enones present as s-trans conformers to provide good yields of the silyl enol ethers of beta-acetylido carbonyl compounds. Typically good substrates are 2-cyclopentenone, 2-cyclohexenone, alpha,beta-unsaturated aldehydes, and beta-alkoxy-alpha-enones. Copper acetylide reagents prepared from CuI and an alkynyllithium give considerably higher yields than those prepared from CuBr or CuCN. Iodotrimethylsilane is by far the most efficient silane, although trimethylsilyl triflate is useful in some cases.