Synthesis of Optically Active β,γ-Unsaturated α-Amino Acids and of α,β-Unsaturated γ-Amino Acids. SN2- vs. SN2’-Dichotomy of the Mitsunobu Amination of Allylic Alcohols
作者:Johann Mulzer、Günther Funk
DOI:10.1055/s-1995-3847
日期:1995.1
Novel and efficient syntheses (6-9 steps, overall yields 10-30%) are described for optically pure β,γ-unsaturated α-amino acids and α,β-unsaturated γ-amino acids, starting from (R)-isopropylidene glyceraldehyde and ethyl (S)-lactate, respectively. The key step is the Mitsunobu reaction of chiral secondary allylic alcohols with phthalimide as the nucleophile, where α,γ allylic transpositions are observed for the first time. The structure-α,γ-ratio-relationship is studied and also the stereochemistry of the allylic transposition. The α-substitution proceeds via clean SN2 inversion, whereas the γ-substitution corresponds to an (E)-anti attack of the nucleophilic with varying stereoselectivities.
本文描述了从(R)-异丙叉甘油醛和乙基(S)-乳酸分别合成光学纯的β,γ-不饱和α-氨基酸和α,β-不饱和γ-氨基酸的新颖且高效的方法(总步骤为6-9步,总收率为10-30%)。关键步骤是手性仲烯丙醇与酞酰亚胺作为亲核试剂的 Mitsunobu 反应,首次观察到α,γ 烯丙基重排现象。研究了结构-α,γ 比例关系以及烯丙基重排的立体化学。α-取代过程通过干净的 SN2 反转进行,而γ-取代对应于亲核试剂的(E)-反向攻击,具有不同的立体选择性。