Asymmetric Synthesis of α-Amino Acids Based on Carbon Radical Addition to Glyoxylic Oxime Ether
作者:Hideto Miyabe、Chikage Ushiro、Masafumi Ueda、Kumiko Yamakawa、Takeaki Naito
DOI:10.1021/jo991353n
日期:2000.1.1
the sultam auxiliary by standard hydrolysis, afforded the enantiomerically pure D-valine (R)-12 without any loss of stereochemical purity. To evaluate the new methodology, a variety of alkyl radicals were employed in the addition reaction which gave the alkylated products 7 with excellent diastereoselectivity, allowing access to a wide range of enantiomerically pure natural and unnatural alpha-amino
报道了基于非对映选择性碳自由基加成乙醛酸亚胺衍生物的α-氨基酸的首次不对称合成。在25°C下,由i-PrI,Bu(3)SnH和Et(3)B在CH(2)Cl(2)中生成的异丙基向非手性乙醛酸肟醚1的区域选择性地在亚氨基上进行。肟醚基的碳原子可得到极佳的C-异丙基化产物2收率。乙醛肟肟1和醛肟醚4的竞争反应表明,乙醛肟肟醚对亲核碳自由基的反应性增强了相邻的吸电子取代基的结构。因此,与未活化的醛肟醚4相反,即使在-78℃下,向乙醛氧基肟醚1的烷基加成也顺利进行。通过使用Oppolzer的樟脑素作为手性助剂,可以实现对乙醛酸肟醚碳自由基加成的高度立体控制。樟脑素衍生物6与异丙基的甲炔基自由基介导的反应在-78℃下得到C-异丙基化产物的96:4非对映异构体混合物7a。通过用Mo(CO)(6)处理还原去除主要的非对映异构体(R)-7a的苄氧基,然后通过标准水解去除sultam助剂,得到对映体纯的D-缬氨酸(R)-