Rasta Resin-PPh₃ and its Use in Chromatography-Free Wittig Reactions

Abstract

Rasta resin-PPh₃, a new heterogeneous polystyrene-based phosphine, has been synthesized and used in one-pot Wittig olefination reactions of aldehydes. In these reactions an excess of rasta resin-PPh₃ was used for the in situ generation of the phosphorane reactant and allowed for isolation of a high yield of very pure alkene product after only filtration and solvent removal. The excellent results obtained in this study are attributed to the flexible nature of the rasta resin structure, which makes it less dependant upon swelling than other heterogeneous polystyrene materials previously used to support phosphine reagents in Wittig reactions.

Key words

polymer-supported reagent - polystyrene - phosphine - phosphorane - Wittig reaction

References and Notes

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See Supporting Information for details.

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General Procedure for Wittig Reactions To a solution of the aldehyde (0.5 mmol) and the alkyl halide (0.75 mmol) in the appropriate solvent (5 mL), was added RR-PPh₃ (1.0 mmol), followed by Et₃N (1.0 mmol). The reaction mixture was stirred at the indicated temperature until TLC analysis indicated that the aldehyde was completely consumed, and then filtered through a plug of silica gel. After washing the polymer with CH₂Cl₂ (2 × 50 mL) the combined filtrate was concentrated in vacuo to afford pure product. All alkene products were characterized by ^¹H NMR and ^¹³C NMR spectroscopy. Steroeoisomeric ratios were determined by ^¹H NMR spectroscopy.