To demonstrate the synthetic potential of this method, a spirocyclic compound bearing an easily removable protective group was subjected to deprotection (Table ). The conventional palladium-catalyzed hydrogenation of 2d, 2l, and 2i afforded the oxalate salt of an amine (3d and 3l) or free amine (3i) almost quantitatively. The same reaction conditions were applicable for the synthesis of oxetane bearing carboxylic acid 3h and an estrone derivative 3j. Again, the structure of 3j was unambiguously confirmed by X-ray analysis. Cycloisomerization affording azetidine. We next explored the azetidine formation of homomethallylamine derivative 4a (Table ). First, the desired azetidine 5a was obtained in 58% yield under the optimal oxetane formation conditions. Solvent screening revealed that toluene was optimal (89%, entries 1-3). Recently, the solvent effect on related reactions has been discussed by considering polarity and viscosity. In our study, the optimal solvents for four-membered heterocycles formation were MTHP for oxetane and toluene for azetidine, which reveals a clear dependency on the nucleophile. The optimal counteranion of the oxidant was found to be hexafluorophosphate (entries 3-5). Unlike in the case of oxetane formation, the yield changed slightly during catalyst screening for azetidine formation. Typically, the desired product (5a) was formed in excellent yields (entries 3, 6-9). When using C4 or C5 and upon reducing the catalyst loading to 3 mol%, we achieved excellent yields (entries 10 and 11). We finally examined the effect of chirality of substrate and ligand on yield. Compared with the result using C4 (entry 10), no significant difference was observed using chiral (R)-4a or ent-C4 (entry 12). When using C5 (the optimal catalyst) and chiral (R)-4a, similar results were achieved (entry 11 and 13). Therefore, the following experiments were performed using a racemic substrate, unless otherwise noted.