Abstract
A novel diazoacetate monomer (1) carrying tert-butyloxycarboryl (Boc) protected D-prolinol ester was designed and synthesized successfully. Molecular weight-controlled polymerization of 1 using the complex of π-allylPdCl coordinated Wei-phos (LR) ligand gives a series of helical polycarbenes (poly-1ms) with well-defined molecular weights (Mns) and low polydispersity (Mw/Mns). Removing the protecting Boc groups on the D-prolinol ester pendants leads to the formation of helical poly-1m-As, which showed high optical activity. Furthermore, the poly-1m-As showed high catalytic ability on asymmetric Michael addition reaction (up to 76% ee and 94/6 dr). Both the enantioselectivity and diastereoselectivity of the Michael addition reaction were increased comparing to D-prolinol as catalyst. Moreover, the helical polycarbene catalyst can be easily recovered and reused at least four times without significant loss of its enantioselectivity and diastereoselectivity.
Highlights
IntroductionAsymmetric organocatalysis, which commonly feature mild reaction conditions and wide functional groups tolerance, attracted considerable attention in recent years [1,2,3]
Efficient Catalyst for AsymmetricAsymmetric organocatalysis, which commonly feature mild reaction conditions and wide functional groups tolerance, attracted considerable attention in recent years [1,2,3].Despite these advantages, higher catalyst loading is necessary in many organocatalyzed reactions [4,5,6]
There is a risk of reducing the catalytic activity and selectivity of the catalysts
Summary
Asymmetric organocatalysis, which commonly feature mild reaction conditions and wide functional groups tolerance, attracted considerable attention in recent years [1,2,3]. Despite these advantages, higher catalyst loading is necessary in many organocatalyzed reactions [4,5,6]. There is a risk of reducing the catalytic activity and selectivity of the catalysts To overcome these limitations, the design and synthesis of polymer which is just serve as a scaffold and can regulate the asymmetric induction effect during the reaction process is highly desirable [12,13]
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