Helical Polycarbenes Bearing <i>D</i>-Prolinol Ester Pendants: An Efficient Catalyst for Asymmetric Michael Addition Reaction
A novel diazoacetate monomer (<b>1</b>) carrying <i>tert</i>-butyloxycarboryl (Boc) protected <i>D</i>-prolinol ester was designed and synthesized successfully. Molecular weight-controlled polymerization of <b>1</b> using the complex of π-allylPdCl coo...
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| Autores principales: | , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/0f38a126ca4d4621a28e428c4bbed41d |
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| Sumario: | A novel diazoacetate monomer (<b>1</b>) carrying <i>tert</i>-butyloxycarboryl (Boc) protected <i>D</i>-prolinol ester was designed and synthesized successfully. Molecular weight-controlled polymerization of <b>1</b> using the complex of π-allylPdCl coordinated Wei-phos (<b>L</b><i><sup>R</sup></i>) ligand gives a series of helical polycarbenes (poly-<b>1</b><sub>m</sub>s) with well-defined molecular weights (<i>M</i><sub>n</sub>s) and low polydispersity (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub>s). Removing the protecting Boc groups on the <i>D</i>-prolinol ester pendants leads to the formation of helical poly-<b>1</b><sub>m</sub>-As, which showed high optical activity. Furthermore, the poly-<b>1</b><sub>m</sub>-As showed high catalytic ability on asymmetric Michael addition reaction (up to 76% <i>ee</i> and 94/6 <i>dr</i>). Both the enantioselectivity and diastereoselectivity of the Michael addition reaction were increased comparing to <i>D</i>-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. |
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