Article ID Journal Published Year Pages File Type
62631 Journal of Catalysis 2007 9 Pages PDF
Abstract

The allylic substitution of (E)-1,3-diphenylallyl acetate (1a) with dimethyl malonate was investigated on Pd/Al2O3 modified by (R)- and (S  )-BINAP, (S,SS,S)-Chiraphos, (R)-C3-Tunephos, and (R)-Solphos. Stable performance of Pd/Al2O3 required its reduction in hydrogen before the allylic substitution reaction, which was carried out under Ar. The enantioselectivity of the Pd/Al2O3-BINAP system [58–60% ee to (S)-2] was independent of the reaction temperature (60 and 120 °C), and only 300 ppm BINAP related to 1a was required. According to UV–vis analysis, only a small fraction of BINAP was adsorbed on Pd/Al2O3. At 120 °C, full conversion and 94% chemoselectivity were achieved in 6 h. For comparison, analogous soluble Pd–BINAP complexes were poorly efficient and afforded low ee to the opposite enantiomer of the product at 60 °C or above. Electron microscopy could detect no restructuring of Pd in Pd/Al2O3 during the reaction. Surprisingly, the addition of BINAP induced a significant rate acceleration (by a factor of almost 7 at 60 °C) and also improved the chemoselectivity of Pd/Al2O3. Among the diphosphine ligands tested, (R)-Solphos was the most effective (67% ee). An important advantage of the Pd/Al2O3–BINAP system is that it can transform not only the allyl acetate 1a, but also the corresponding allyl alcohol 1b without the application of any additive.

Related Topics
Physical Sciences and Engineering Chemical Engineering Catalysis
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