Optically active diastereomers were prepared by diastereomeric salt formation with the chiral base, l-tyrosine hydrazide, to provide Cbz or Boc protected 4-cis-d-pipecolic acid derivatives in >98% ee. Subsequent esterification followed by sodium methoxide catalyzed epimerization provided the isomeric 4-trans-l-pipecolic esters. In addition, an efficient synthesis of 4-phenyl-cis-pipecolic acid is described
描述了对映体富集的4-苯基,4-叔丁基和4-异丙基
胡椒酸的合成和拆分。通过与手性碱1-
酪氨酸酰
肼形成非对映异构体盐来制备旋光非对映异构体,以提供大于98%ee的Cbz或Boc保护的4-顺-d-
哌酸衍
生物。随后的酯化,然后是
甲醇钠催化的差向异构化,提供了异构体4-反式-1-哌库酸酯。另外,描述了4-苯基-顺式-
哌酸的有效合成。