We began our study by examining the formal (5+1) cycloaddition of diazooxindole 1a with imidazolidine 2a (Scheme 2, see Supporting Information for details). Several noble-metal catalysts including silver, gold, palladium and rhodium were initially evaluated. Gratifyingly, by using Rh2(esp)2 as the catalyst in CH2Cl2 at room temperature, a slow addition of 1a to 2a led to the desired spirooxindole-piperazine product 3 in 90% yield (condition A). Besides, some base-metal catalysts emerged in the activation of diazo compounds, such as copper and iron, were also tested. Cu(OTf)2 proved to be a competent catalyst, providing product 3 in 60% yield in CH2Cl2 at room temperature, while other copper and base-metals resulted in very slow or no reaction. A number of other reaction parameters including solvent, temperature and catalyst loading were then varied, but the key advance was an increased temperature, offering product 3 in 85% yield at 80 o C in a sealed tube (condition B). The structure of 3 was confirmed by X-ray diffraction analysis (CCDC 2211107). Scheme 2. Condition optimizations.