Green Chemistry
Paper
Ent-crystals of the previous crystallization were added and crys-
tallization was observed. The suspension was further cooled to
2 °C 1 °C and filtered over a büchi filter with a paper filter.
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SCPA: 22.9 g, 66%. Spectral data were in accordance with the
literature.39
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Conclusions
Optimization of a novel route towards DHPPA has been dis-
closed. The chlorination of ethyl(R)-lactate has been studied in
detail. The formation of intermediates and side products has
been minimized by adjustment of reagent stoichiometry,
temperature and choice of catalyst. The highest ee (99%) was
reached with the use of pyridine. The best overall result with a
yield of 85% after distillation and still 98% ee was reached
with the use of dmf at a starting temperature of 65 °C. These
conditions are considered to be indicative for production on
an industrial scale. The etherification towards DHPPA gave a
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In terms of green chemistry, significant improvements com-
pared to existing practice have been made. We believe that the
process presented here is economically feasible and even
advantageous compared to current practice. The chiral starting
material is a bio-based building block made through the
process of fermentation. The further process has significant
improvements in waste reduction and toxicity reduction. The
resulting products are made with higher yields, higher selecti-
vity and are of a higher quality compared to current practice.
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Acknowledgements
We would like to thank Jan van Krieken and Kees van der
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