Proline: An essential amino acid as effective chiral organocatalyst

Abstract

(A) If a nitroso compound is used as aldol acceptor, α-aminoxylation affords versatile synthons for natural product synthesis. (B) If an additive is used, proline can catalyze the Michael addition of nitroalkanes to cyclic enones. In ionic liquid, addition of thiophenols to chalcones is catalyzed by L-proline (up to 91% yield, ee not given). (C) Asymmetric organocatalysis is a powerful tool to synthesize sugars in two steps without protection or deprotection reactions, and to realize excellent enantiomeric excesses. (D) Cascade reactions such as the combination of α-amination of an aldehyde and an aldol reaction, are effectively catalyzed by L-proline. (E) New promising reactions are also in progress. Córdova and co-workers have developed an α-oxidation reaction. α-Fluorination of aldehydes and ketones with Selectfluor have been developed by Enders and Huttl to afford the fluorinated cyclohexanone in 43% yield and with 29% ee. © Georg Thieme Verlag Stuttgart.