This study revealed that 4-(trimethylsilyl)-3-butyn-2-one was an effective dipolarophile in the [3+2] cycloaddition reaction with cycloimmonium salts to obtain non-silicon adducts, namely 1-acetylindolizines. In some cases, two possible isomeric trimethylsilyl-containing adducts were also obtained. The structure of these silylated adducts has been found by X-ray crystallography to be 1-acetyl-2-trimethylsilyl-indolizines and 1-trimethylsilyl-2-acetylindolizines. The performance of 4-(trimethylsilyl)-3-butyn-2-one was compared to that of 3-butyn-2-one in the [3+2] cycloaddition reaction. The resulting 1-acetyl or 2-acetylindolizines were compared to previously described 3-acetyl or 1-carboxyethylindolizines in terms of biological potential to inhibit the NCI-60 cancer cell growth in vitro.