Chiral Diols

Chiral Diols

Among the many chiral compounds, chiral diols are compounds containing two hydroxyl groups in a chiral molecule. It can not only participate in many life activities but also can be used as a very important chiral cleavage and chiral intermediate. Chiral diols are also a wide range of chiral ligands that are widely used. Moreover, they are also raw materials for the preparation of chiral compounds such as chiral diamines and diphosphines. It plays an important role in the fields of medicine, chemical industry, food, agriculture, and functional materials.

Application

Chiral diols are widely used as chiral ligands and chiral catalysts in asymmetric synthesis. The chiral ligand can provide the chiral environment required for the reaction, and the chiral catalyst is a metal organic compound formed by the complex of a chiral ligand with a central metal. Therefore, it can be widely used in asymmetric catalytic reactions. For example, asymmetric hydrogenation, asymmetric oxidation, asymmetric aldol condensation, asymmetric Reformatsky reaction, and the like.

Production

The preparation methods of common chiral diols include enantioselective reduction, chiral resolution, olefin epoxidation ring opening, olefin asymmetric di-lightening, aldehyde ketone reduction coupling link, and chemical conversion of chiral compounds.

• Enantioselective reduction reaction：The corresponding diol can be obtained by reduction of the diketone using a borane reagent. If some chiral catalyst is added during this process, an enantioselective reduction can be carried out. For example, (2, R, R)-7 can be obtained by reducing diphenylethylenedione using a chiral boron oxazolidine as a catalyst.
• Chiral split：Chiral resolution of racemates is an important method for obtaining photoactive substances by chemical means and is often used in the preparation of chiral diols.
• Olefin epoxidation ring opening reaction: The epoxidation ring opening of olefins is an important method for the preparation of chiral 1,2-diols. Some scholars have used Co-Salen catalyst 9 to catalyze the epoxide 10, 11, 12, and the chiral diol formed under benzoic acid as a nucleophile is smoothly converted to 13. 14.15. Both product yield and ee value are relatively high.
• Chemical conversion of chiral compounds: Conversion using some natural, common chiral reagents is also a common preparation of chiral diols. For example, 1,2-cyclopentanediol and useful chiral ligands can be synthesized starting from natural diethyl tartrate.
• Aldehyde and ketone reduction coupling synthesis: Reductive coupling of aldehydes and ketones to prepare enantiomerically pure sterols is a very practical method for the synthesis of chiral 1,2-diols. Many useful catalysts have been applied to the reaction, as shown in Figure 1.

  Figure 1. Preparation of chiral diols by aldehyde and ketone reduction coupling synthesis

• Asymmetric Dihydroxylation of Alkenes (AD Reaction): It is a process of oxidizing an alkene to form an ortho chiral diol under the action of a chiral catalyst. Some scholars pioneered this method for the first time and thus won the 2001 Nobel Prize in Chemistry. The main purpose is to use the cinchona alkaloid derivative as a catalyst for the tetragonal ligand to catalyze the reaction of olefin.
• Biosynthesis：The essence of the preparation of a chiral compound by a biological method is a chiral substance which converts a racemic derivative or a latent chiral compound into a single configuration by using a microbial whole cell or an enzyme as a catalyst. The main biocatalysts for the preparation of chiral diols by biological methods are dioxygenase, epoxide hydrolase, and reductase.

References

1. Prasad, K. R. K.; Joshi, N. N.(1996). “Stereoselective Reduction of Benzils: A New Convenient Route to Enantiomerically Pure 1,2-Diarylethanediols.” J. Org. Chem. 61, 3888-3889.
2. Murata, K.; Okano, K.; Miyagi, M.”(1999). Stereoselective Synthesis of Chiral Hydrobenzoins via Asymmetric Transfer Hydrogenation of Benzils. “ Org. Lett.1, 1119-1121.
3. Wu, X.; Li, X.; Zanotti-Gerosa. (2008). ”IrIII-Catalyzed Asymmetric Transfer Hydrogenation of Ketones in Water. “Chem. Eur. J. 14, 2209-2222.