Asymmetric Synthesis of α-Amino Acids: Preparation and Alkylation of Monocyclic Iminolactones Derived from α-Methyl <i>trans</i>-Cinnamaldehyde
作者:Ta-Jung Lu、Cheng-Kun Lin
DOI:10.1021/jo801514g
日期:2008.12.19
monocyclic iminolactones 14a and 14b have been prepared. The chiral auxiliary 12 was obtained from alpha-methyl-trans-cinnamaldehyde through reduction, methylation, Sharpless asymmetric dihydroxylation, and oxidation in 87% overall yield. Esterification of compound 12 with the respective protected amino acids followed by deprotection and cyclization provided the corresponding iminolactones, each in 82%
已经制备了两种新颖的手性单环亚氨基内酯14a和14b。通过还原,甲基化,Sharpless不对称二羟基化和氧化从α-甲基-反式肉桂醛获得手性助剂12,总产率为87%。用各自的被保护的氨基酸酯化化合物12,然后去保护和环化,提供了相应的亚氨基内酯,每一个的总产率为82%。亚氨基内酯14a的烷基化以良好的产率(78-99%)和优异的非对映选择性(de> 98%)提供了α-甲基-α,α-二取代的产物15和16。亚氨基内酯14b的烷基化提供了高产率(51-86%)但中等非对映选择性(43-56%)的α-苄基-α,α-二取代产物15a,16b,17和18。当HMPA或DMPU用作助溶剂时,亚氨基内酯14b的烷基化速度加快,产率提高(56-99%),非对映选择性(50-83%)。二烷基化亚氨基内酯的水解以良好的收率(80-98%)和高的对映体过量(98-99%)产生了α,α-二取代的α-氨基酸,并具有