From Biomass to Chiral Chemicals via Chemocatalysis: Advances and Prospects^†

Optically pure chiral chemicals are important building blocks with widespread applications across multiple scientific and industrial domains such as in pharmaceuticals, agrochemicals, and food, especially acting as precursors to synthesize biodegradable polymers. As an alternative to fossil resources, renewable lignocellulosic biomass has been used to access chiral chemicals, due to the versatile inherent stereostructures and multiple functional groups, such as hydroxyl, carbonyl, and phenyl ether groups. Typically, as the two main units of (hemi)cellulose components in lignocellulosic biomass, D-xylose and D-glucose bear multiple chiral centers (e.g., 2R-3S-4R for D-xylose and 2R-3S-4R-5R for D-glucose). Lignin bears β-O-4 linkages, exhibiting (R,S/S,R) or (R,R/S,S) stereocenters at the side-chain α and β carbon atoms. The valorization of biomass into optically pure chiral chemicals is vital for developing a more sustainable future. This review discusses the production of typical chiral chemicals derived from biomass through chemocatalysis, including lactones (e.g., R/S-valerolactone), carboxylic acids (e.g., D/L-glyceric acid, D/L-lactic acid), polyols (e.g., tetrose), furans, oligosaccharides, and others. Two strategies are generally employed. One approach involves first producing achiral platform chemicals from biomass, followed by the introduction of asymmetric catalysts to reconstruct stereocenters. The second relates to selectively preserving one or more inherent stereocenters in the natural biomass structure during complex cascade reactions in which biomass feedstock acts as a “chiral pool", thus eliminating the establishment of stereocenter. The feedstock, methods employed, and enantioselectivity and applications of the target chiral chemicals are discussed. Despite these advances, the synthesis of optically pure chemicals from biomass is still in its infancy. The coming decade presents both extraordinary challenges and opportunities in biomass-derived chiral chemistry. Future research should be focused on: (1) integrating well-established asymmetric catalysis techniques and methods with biomass’ inherent chiral pools, presenting an unprecedented opportunity to expand the chemical space of sustainable chiral compounds; (2) mastering polyfunctional complexity of chiral chemicals through holistic utilization of biomass’ multichiral centers; (3) unlocking lignin’s stereochemical treasury that represents the next frontier in biomass valorization.