Organocatalyzed Step-Growth Polymerization through Desymmetrization of Cyclic Anhydrides: Synthesis of Chiral Polyesters
Résumé
The polymerization of prochiral bis-anhydrides with diols catalyzed by a cinchona alkaloid was shown to provide chiral polyesters in good yields and with high levels of stereocontrol. The structures of the polyesters were determined by H-1 and C-13 NMR analyses, whereas their size was estimated by both size-exclusion chromatography (SEC) and MALDI-TOF mass spectrometry, which indicated that moderate degrees of polymerization were attained through this step-growth polymerization. The enantioselectivity of the process was evaluated by using chiral HPLC analysis of the bis-lactones resulting from a controlled chemoselective degradation of the polyesters. The best stereocontrol was reached for oligomers formed from bis-anhydride and diol monomers bearing rigid aromatic spacers between the reactive functional groups. In this case, average enantioselectivities were comparable to those observed during ring-opening of simple anhydrides with similar alcohols. In contrast, the use of more flexible spacers between reactive entities generally led to lower levels of stereocontrol.
Mots clés
ENANTIOSELECTIVE CYCLOPOLYMERIZATION
MUKAIYAMA ALDOL REACTION
ALPHA-OLEFINS
anhydrides
desymmetrization
enantioselectivity
organocatalysis
polyesters
polymerization
ASYMMETRIC-SELECTIVE POLYMERIZATION
VIBRATIONAL CIRCULAR-DICHROISM
RING-OPENING POLYMERIZATION
FUNCTIONAL THEORY CALCULATIONS
OPTICALLY-ACTIVE POLYMERS
(RS)-ALPHA-METHYLBENZYL METHACRYLATE
CHROMATOGRAPHIC-SEPARATION