... Tetrahedron Letters. Volume 50, Issue 4, 28 January 2009, Pages 492–494. ... (R)-Pipecolic acid and (R)-proline were obtained, respectively, in 50% yield and 94% ee from 6,6-dimethoxyhexanal and in 41% yield and 84% ee from 5,5-dimethoxypentanal. ...