One-pot synthesis of enantiopure syn-1,3-diacetates from racemic syn/anti mixtures of 1,3-diols by dynamic kinetic asymmetric transformation

A one-pot synthesis of enantiomerically pure syn-1,3-diacetates starting from readily accessible racemic diastereomeric mixtures of 1,3-diols has been realized by combining (i) enzymatic transesterification, (ii) ruthenium-catalyzed epimerization of a secondary alcohol in a diol or diol monoacetate, and (iii) intramolecular acyl migration in a syn-1,3-diol monoacetate. The in situ coupling of these three processes results in an efficient enantioselective synthesis of acyclic syn-1,3-diacetates via combined deracemization–deepimerization and constitutes a dynamic kinetic asymmetric transformation concept. Several differently substituted unsymmetrical, acyclic syn-1,3-diacetates were obtained in yields up to 73% with excellent enantioselectivities (>99%) and good diastereomeric ratios (>90% syn)

Direct enantio-convergent transformation of racemic substrates without racemization or symmetrization

Asymmetric reactions that transform racemic mixtures into enantio-enriched products are in high demand, however, classical kinetic resolution (KR) can afford enantiopure compounds in <50% yield even in an ideal case. Many deracemization processes thus have been developed including dynamic kinetic resolution (DKR) and dynamic kinetic asymmetric transformation (DYKAT), which can provide enantio-enriched products even after complete conversion of the racemic starting materials; however, these dynamic processes require racemization or symmetrization of the substrates or intermediates. We demonstrate a first chemical direct enantio-convergent transformation without racemization or symmetrization process. The copper(I)-catalysed asymmetric allylic substitution of a racemic allyl ethers afforded a single enantiomer of an α-chiral allylboronates with complete conversion and high enantioselectivity (up to 98% ee); one enantiomer of the substrate undergoes an anti-SN2'-type reaction whereas the other enantiomer reacts via a syn-SN2' pathway. The products, α-chiral allylboronates, cannot be prepared by dynamic procedures, were used in construction of all-carbon quaternary stereocentres

Enantioselective hydrolysis of racemic styrene oxide by epoxide hydrolase of Rhodosporidium kratochvilovae SYU-08

Enantioselective hydrolysis for the production of chiral styrene oxide was investigated using the epoxide hydrolase activity of a newly isolated Rhodosporidium kratochvilovae SYU-08. The effects of reaction parameters - buffer type, pH, temperature, initial substrate concentrations, phenyl-1,2-ethanediol concentrations on hydrolysis rate, and enantioselectivity - were analyzed. Optically active (S)-styrene oxide with an enantiomeric excess higher than 99 % was obtained from its racemate, with a yield of 38 % (theoretically 50% maximum yield) from an initial concentration of 80 mM