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Updated: Jun 23, 2026

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
Highly Active and Isoselective Ion-Paired Hexadentate Amino-bisphenolate Alkali Metal Complexes for the Ring-Opening
Yang Huang1, Hehua Li1, Haiyan Ma1
1Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, People's Republic of China.
Abstract:
Novel ion-paired alkali metal complexes Na1-Na4 and K1, supported by hexadentate amino-bisphenolate ligands incorporating two pendant heterocyclic rings, were synthesized. In the solid state, the multidentate ligand in Na1 and Na4 coordinates to the metal center in a pentadentate fashion, leaving one heterocyclic ring uncoordinated; in solution, however, these complexes adopt symmetric and fluxional structures. Using benzyl alcohol (BnOH) as an initiator, all complexes efficiently catalyzed the ring-opening polymerization (ROP) of rac-LA at room temperature, delivering isotactically biased PLAs with high activities (TOF up to 37917h-1). At 223 K, the sodium complexes Na1-Na4 exhibited significantly enhanced isoselectivities (Pm = 0.78-0.89), while the potassium complex K1 remained less stereoselective (Pm = 0.64). Among them, Na1 displayed the highest activity and isoselectivity (TOF up to 2407 h-1; Pm = 0.87-0.89). Under optimized conditions ([rac-LA]0/[Na1]0/[BnOH]0 = 2500/1/2), Na1 afforded high-molecular-weight isotactic PLA (Mn = 134 kg/mol, Pm = 0.89). Further decreasing the temperature to 203 K improved the isoselectivity of Na1 to Pm = 0.92 with sufficient activity still retained (TOF = 245 h-1). Based on the ROP studies of L-LA, NMR-scale reactions, and MALDI-TOF mass spectrometric analysis of typical oligomers, it is proposed that at low temperature the ROP of rac-lactide is initiated via a ligand-assisted activated-monomer mechanism in the presence of BnOH.
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