Stereoselective Syntheses of l-Pipecolic Acid and (2S,3S)-3-Hydroxypipecolic Acid from a Chiral N-Imino-2-phenyl-1,2-dihydropyridine Intermediate

Stereoselective syntheses of l-pipecolic acid and (2S,3S)-3-hydroxypipecolic acid were achieved from a chiral N-imino-2-phenyl-1,2-dihydropyridine intermediate. The 3-hydroxy substituent of the latter amino acid was introduced by hetero-Diels−Alder reaction of singlet oxygen with the 1,2-dihydropyridine.