The efficient and direct synthesis of protected biaryl amino acids, including dityrosine (50% overall yield over 3 steps), by Negishi cross-coupling of the serine-derived organozinc reagent 4 with iodo- and di-iodobiaryls, is reported. An improved, although still not perfect, diiodination of 2,2′-biphenol has been achieved using NMe3BnICl2–ZnCl2. Protection of phenolic hydroxyl groups as acetates, rather than benzyl ethers, is required for efficient cross-coupling, and evidence for acetyl migration has been observed during debenzylation of a substituted 2-acetoxy-2′-benzyloxybiaryl. Aromatic C–I to C–Cl conversion has been detected as a minor reaction pathway in the palladium-catalyzed coupling of aryl iodide 3b with organozinc reagent 4.
据报道,通过
丝氨酸衍生的
有机锌试剂 4 与
碘和二
碘芳基的 Negishi 交叉偶联,高效直接地合成了受保护的双芳基
氨基酸,包括双
酪氨酸(3 个步骤的总收率为 50%)。使用 NMe3BnICl2-ZnCl2 实现了 2,2′-联
苯酚的改进型二
碘化反应,尽管还不够完美。
酚羟基作为
乙酸酯而不是苄基醚进行保护是高效交叉偶联的必要条件,在取代的 2-乙酰氧基-2′-苄氧基芳基的去苄基化过程中观察到了乙酰基迁移的证据。在
钯催化的芳基
碘化物 3b 与
有机锌试剂 4 的偶联反应中,发现芳香族 C-I 到 C-Cl 的转化是一个次要的反应途径。