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D. J. Bayston et al. / Tetrahedron: Asymmetry 9 (1998) 2015–2018
Fig. 2.
to 2-phenethanol indicating that a homogeneous catalyst was not responsible for ketone reduction. This
reaction also confirmed that no leaching of catalyst from the polymer was occurring.
We have also used the polymer bound catalyst to reduce 2-chloroacetophenone (Fig. 2). Our best
conditions for this transformation were found to be ligand (1S,2S)-6b in DMF using HCO H:Et N as the
2
3
9
source of hydrogen. (R)-2-Chloro-1-phenethanol was obtained in 90% yield and 95.3% ee.
In summary, we have developed a practical route to a heterogeneous enantioselective transfer
hydrogenation catalyst. The reduction of acetophenone has been examined and a reusable catalyst has
been identified. The reduction is best performed neat in HCO H:Et N for polymer 6a containing the
2
3
polyethyleneglycol spacer unit. A cosolvent such as DMF or CH Cl is necessary to attain good reactivity
2
2
for the simple polystyrene based catalyst 6b. The reactivity of the polymeric catalyst on reuse decreases
and after three uses the reaction time for good conversion becomes impractically long although the
enantiomeric excesses remain high. Investigation into further reuse of this catalyst and its application
to industrially useful transformations is currently in progress.
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. Enantiomeric excess was determined by HPLC on a Chiralcel OD column. Absolute configuration was determined by
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