Pyrrolidine-2-carboxylic acid (L-proline)

L-Proline (I) catalyzes the asymmetric aldol reaction between acetone and various aldehydes. In the case of hydroxy acetone, it gives anti-diols in excellent diastereo- and enantioselectivities. L-Proline catalyzes the Michael reaction of ketones with nitro olefins to provide a variety of chiral Michael addition products. L-Proline catalyzes asymmetric the three component coupling involving Mannich reaction of acetone aldehydes and aryl amines to give β-amino ketones. In case of hydoxyacetone it gives α-hydroxy β-amino ketones in good to excellent ee. This reaction complements the Sharpless asymmetric aminohydroxylation. L-Proline catalyzes Mannich type reaction of protected α-imino ethyl glyoxylate with a variety of ketones to provide functionalized α-amino acids in high enantioselectivities. L-Proline catalyzes α-amination of ketones by applying azodicarboxylate as nitrogen source to give chiral α-hydrazino, α-amino ketones, and alcohols. Recently, I has proved to be the best catalyst for asymmetric Robinson annulation.