γ‐Pyronecarbaldehyde‐Based Practical Asymmetric Catalytic Synthesis of Chiral 2,4‐Dihydroxycarboxylic Acids and α‐Hydroxy‐γ‐lactones

Biomass derived γ‐pyrone‐2‐carbaldehydes were proposed as robust heterocyclic platform for carrying out organocatalytic asymmetric cross‐aldol reactions with various aldehydes and ketones in high yield with excellent diastereoselectivity and enantioselectivity. Origins of efficient stereoinduction were revealed by quantum‐chemical calculations of four possible transition states. The products were converted to synthetically useful chiral 2,4‐dihydroxy carboxylic acid derivatives via protection/deprotection and RuIII‐catalyzed oxidative fragmentation steps without racemization of stereogenic centers. The developed approach was applied for asymmetric synthesis of chiral pantolactones, valuable precursors of biologically active substances and natural products, and for synthesis of Dexpanthenol, a medication used for treating defects in the barrier function of skin.