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. All four stereoisomers of the desired 1,3-diol product are accessible via a sequential flow approach.
The catalyst loading in the narrow range between 0.5 and 10 mol % determines whether an enantioselective organocatalytic aldol reaction proceeds under kinetic or thermodynamiccontrol; high conversions and ee values can be achieved with low catalyst loadings (see scheme). Since the reaction is carried out in water, it can be combined with a biocatalytic reduction for the one‐pot synthesis of 1,3‐diols