The conjugate additions of homochiral lithium (R)-N-benzyl-N-α-methyl-4-methoxybenzylamide to tert-butyl 3-(3-pyridyl)- and tert-butyl 3-(4-pyridyl)-prop-2-enoates proceed in 84% de, and after subsequent recrystallisation and oxidative N-deprotection furnish the (S)-3-(3-pyridyl)- and (S)-3-(4-pyridyl)-β-amino acid derivatives in 97% ee and 98% ee respectively. Conjugate additions of lithium N-benzyl-N-α-methyl-4-methoxybenzylamide to tert-butyl 3-(2-pyridyl)prop-2-enoates proceed with low levels of diastereoselectivity unless the 3-(2-pyridyl) ring is substituted. Application of this methodology allows the asymmetric synthesis of (R)-tert-butyl 3-(2-chloro-3-methoxymethoxy-6-pyridyl)-3-aminopropanoate, the protected β-amino ester component of kedarcidin, in 97% ee.
同手性的(R)-N-苄基-N-δ-甲基-4-甲氧基苄基酰胺
锂与 3-(3-
吡啶基)-叔丁基和 3-(4-
吡啶基)-丙-2-烯酸叔丁基酯的共轭加成反应以 84%de、然后经过重结晶和氧化 N-保护,得到 (S)-3-(3-
吡啶基)-和 (S)-3-(4-
吡啶基)-δ-
氨基酸衍
生物,ee 值分别为 97% 和 98%。除非 3-(2-
吡啶基)环被取代,否则 N-苄基-N-δ-甲基-4-甲氧基苄基酰胺
锂与 3-(2-
吡啶基)丙-2-烯酸叔丁酯的共轭加成具有较低的非对映选择性。应用这种方法可以不对称地合成(R)-3-(2-
氯-3-甲氧基甲氧基-6-
吡啶基)-
3-氨基丙酸叔丁酯,即凯达西汀的受保护δ-
氨基酯成分,ee值为97%。