Quantum studies on the deprotection mechanism of 2-phenyl-1,3-dioxolane catalyzed by α,β-cyclodextrins

The inclusion processes of α,β-cyclodextrins (α,β-CDs) with 2-phenyl-1,3-dioxolane (d), its dihydrate (e) and tetrahydrate (f) have been investigated using PM3, B3LYP and ONIOM2 methods. Solvent effects on the inclusion processes have been corrected using Onsager continuum solvation model combining with B3LYP/6-31G(d). The calculated results indicated that the inclusion complex of head down had an obvious energy advantage over the corresponding head up, and the continuum solvent effect disfavored the formation of inclusion complexes in water. The stability difference between (f)/α-CD head down (−2.90 kcal mol−1) and (f)/β-CD head down (−21.36 kcal mol−1) was closely relative to the yield and the selectivity of the studied deprotection reaction. The deprotection reaction of (d) in water might proceed in a three-step mechanism as follows. Firstly, (d) integrated with four H2O molecules to form the tetrahydrate (f). Then, (f) entered the hydrophobic cavity of α,β-CDs from secondary hydroxyl rim (S–OH) to yield the complexes of (f)/α,β-CDs head down with different stabilities. Finally, the more stable (f)/β-CD head down were transformed into benzaldehyde, H2O and β-CD.