Zinc Triflate as Lewis Acid in Nucleophilic Addition to Cyclic N-Acyliminium Ions

Zinc triflate-mediated nucleophilic addition of allytrimethylsilane, silyl enol ethers and terminal acetylenes to cyclic Nacyliminium ions at room temperature in CH2CI2 is described. The corresponding (alpha)-substituted heterocycles were obtained in moderate to good yields. The versatility of this reagent was demonstrated in the one-pot generation of the N-acyliminium ion and the zinc alkynylide species, followed by their coupling reaction to afford propargylic adducts in moderate yields.