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Polymer-Bound Lewis Acids

Chemfiles Volume 5 Article 11

Lewis acids are important catalysts for many types of transformations in organic chemistry. Lanthanide salts serve as mild alternatives to traditional hard Lewis acids. Reactions catalyzed by the polymerbound lanthanide Lewis acids include acetalization, aldol reaction and allylation of aldehydes, nucleophilic addition to imines, aza- Diels–Alder reactions, and ring opening of epoxides.1 Polymer-bound reagents react the same as the solution-phase equivalent and have the added advantage of ease of handling, simplified reaction workup and, in some cases, recyclability.

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Ytterbium(III) Polystyrenesulfonate



Typical Experimental Procedure for Ring Opening of Epoxides



Styrene oxide (0.12 mL, 1 mmol) and ytterbium(III) polystyrenesulfonate polymer-bound (100 mg, 0.056 mmol) were mixed in methanol (1 mL), and stirred at room temperature overnight (16 h). TLC showed that the reaction went to completion. The reaction was filtered and the resin washed with methanol (2 × 1 mL). The combined solution phases were evaporated to give 2-methoxy-1- phenylethanol a colorless oil (151 mg, 100%).

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Scandium(III) Bis(trifluoromethanesulfonate), Polymer-Bound

One of the important transition metal Lewis acid catalysts is scandium(III) bis(trifluoromethanesulfonate), which is widely used in carbon–carbon bond and carbon–heteroatom bond formation.2


Typical Experimental Procedure for Addition of Allyl Group to Esters



Ethyl benzoylformate (178 mg, 1 mmol), tetraallyltin (282 mg, 1 mmol) and scandium bis(trifluoromethanesulfonate), polymerbound(10 mg, 0.0068 mmol) were mixed in water (6 mL). The mixture very quickly became cloudy and was stirred at room temperature overnight. Then ether (20 mL) was added and the mixture was passed through a silica gel pad. The organic layer was separated, dried, and evaporated to afford a white solid (205 mg, 95% yield). The structure was confirmed by 1H NMR.

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Materials

     

References

  1. Dondoni, A.; Massi, A. Tetrahedron Lett. 2001, 42, 7975. Yu, L.; Chen, D.; Li, J.; Wang, P. G. J. Org. Chem. 1997, 62, 3575.
  2. Kobayashi, S.; Sugiura, M.; Kitagawa, H.; Lam, W. W. L. Chem. Rev. 2002, 102, 2227. Kobayashi, S.; Kitagawa, H.; Matsubara, R. J. Comb. Chem. 2001, 3, 401.

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