Combination of Asymmetric Organo- and Biocatalysis in Flow Processes and Comparison with their Analogous Batch Syntheses
Lukas Schober (Bielefeld University)
Fabio Tonin (TU Delft - BT/Biocatalysis)
Ulf Hanefeld (TU Delft - BT/Biocatalysis)
Harald Gröger (Bielefeld University)
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Abstract
A sequential-type as well as a tandem-type chemoenzymatic flow cascade combining an organocatalytic aldol reaction and a biocatalytic reduction to form stereoselectively a 1,3-diol with two stereogenic centers were developed. Initially, a comprehensive screening of 24 alcohol dehydrogenases was carried out and the identified candidates were applied in different multi-step flow cascades. All four stereoisomers of the desired 1,3-diol product are accessible via a sequential flow approach with product formation-related conversions of up to 76 % over two steps, isolated yields of up to 64 % and enantiomeric excess of >99 % in all cases. In addition, a tandem-type flow process, performing both reaction steps simultaneously, was established leading to 51 % conversion with >99 % ee and 8 : 1 d.r. and representing a combination of the fields of asymmetric chemocatalysis, biocatalysis and flow chemistry.
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