Kinetic resolution of sulphoxides by chiral poly(N-alkyliminoalanes)

Abstract
Kinetic resolution of racemic sulphoxides by chiral poly[N-(1-phenylethyl)iminoalanes](PIA-PHETs) from (+)- or (–)-1-phenylethylamine is described. For p-tolyl mesityl sulphoxide in the temperature range between –25 and +85 °C, optical yields increase with temperature to an upper limit of between 55 and 70 °C, with enantiomeric enrichments up to ca. 75%. It is shown that, among the three molecular species of PIA-PHET (closed-cage tetramer, closed-cage hexamer and open-cage tetramer), only the last is chemically active and capable of chiral recognition. Reactions follow second-order kinetics (first-order in sulphoxide, first-order in open PIA-PHET tetramer). The particular molecular structure of the latter probably accounts for the high degree of chiral recognition at high temperature.

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