Abstract
Metal/lipase-combo catalyzed dynamic kinetic resolution (DKR) of racemic chiral alcohols is a general and practical process to obtain the corresponding enantiopure esters R with quantitative conversion. The use of known Ru-catalysts as well as newly developed homogeneous and heterogeneous metal catalysts (Fe, V) contributed to make the DKR process more sustainable and to expand the substrate scope of the reaction. In addition to classical substrates, challenging allylic alcohols, tertiary alcohols, C1-and C2-symmetric biaryl diols turned out to be competent substrates. Synthetic utility further emerged from the integration of this methodology into cascade reactions leading to linear/cyclic chiral molecules with high ee through the formation of multiple bonds, in a one-pot procedure.
Highlights
Two enantiomers of a chemical compound may have different biological activity resulting from the interaction with chiral environment in biological systems
The application of metal, organo- or bio-catalysis have played a role in developing this type of strategy, whereas, the multi-catalytic approach based on the concurrent activity of different catalysts is a less exploited concept due to possible incompatibilities between the different catalytic systems used [52,53]
The examples collected in this review show that metal/enzyme combo-catalyzed dynamic kinetic resolution continues to be a powerful tool for the quantitative transformation of racemic alcohols into the corresponding (R)-esters
Summary
Two enantiomers of a chemical compound may have different biological activity resulting from the interaction with chiral environment in biological systems. The co-catalyzed DKR of the tertiary alcohol in the presence of CAL-A from Candida antartica lipase A and vinyl acetate led to the desired (R)-acetate in 77% yield and excellent ee value (>99%) (Scheme 8) Stepwise addition of both the catalysts during the reaction allowed to overcome the inactivation of the enzyme due to long reaction times (312 h). The co-catalyzed DKR of chiral benzyl alcohols with CAL-B and vinyl acetate worked well independently on the electronic nature of the aromatic substituents (H, Me, Cl, MeO) (2–4 h, up to 89% yield and 99% ee) Both catalysts were separated and re-used six times without loss of efficiency. Ru(OH) as co-catalysts, the use of 12 gave similar yield and better enantioselectivity [17]
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