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(2-hydroxypropyl-4-nitrophenyl phosphate)catalyzed by mononuclear zinc-containing complexes are investigated in the paper via a theoretical approach.The general-base-catalyzed(GBC)mechanism and the special-base-catalyzed(SBC)mechanism are thoroughly discussed in the paper and the calculations indicate a SBC mechanism(also named as direct nucleophilic attack mechanism)when the cyclization of HpPNP is promoted by the Zn: [12]aneN3 complex.The ligand effect is considered by involving two different-sized catalysts(Zn: [12]aneN3 and Zn: [9]aneN3)and the results shows that the increased-sized catalyst is more competitive for a lower energy barrier and significant mechanistic preference to the SBC mechanism.The solvent medium effect is also explored and the reduced polarity/dielectric constant solvents,such as light alcohols methanol and ethanol,are more favorable.Ethanol is a good candidate as a solvent medium for its low dielectric constant and more importantly,the corresponding stronger Lewis base.Our proposed mechanisms are favor of associative unsymmetrical concerted pathways.Our theoretical results are consistent with and well interpret the experimental observations [1,2] and more importantly,provide suggestions on the catalyst design and the selection of reaction conditions.