Highly Enantioselective Synthesis of Pipecolic Acid Derivatives via an Asymmetric Aza-Diels-Alder Reaction
Very high asymmetric induction is observed in the aza-Diels-Alder reaction between dienes and the imine (R)-PhMeCH-N=CHCO2PhMen* (where PhMen* = 8-phenylmenthyl), which bears matched auxiliaries on nitrogen and on the ester; reactions in trifluoroethanol, in the presence of trifluoroacetic acid (1 equiv.), give substituted pipecolic acid derivatives in ca 50percent isolated yield, with only a single regio- and diastereo-isomer of the cycloadduct detectable in all cases (d.e. > 95percent).
Bailey, Patrick D.,Londesbrough, Derek J.,Hancox, Timothy C.,Heffernan, John D.,Holmes, Andrew B.