The simple and highly enantioselective methanolysis of cyclic meso-anhydrides mediated by cinchona alkaloids leads to a broad variety of dicarboxylic acid mono-methyl esters with up to 99% ee. From these products, unnatural N-protected β-amino esters can be obtained by means of Curtius degradation of the corresponding acyl azides. Subsequent cleavage of the protecting groups leads to the free β-amino acids in excellent yields. By enantiomer differentiating opening of racemic anhydrides, synthetically highly useful regioisomeric amino acid esters become readily available.
由
金鸡纳
生物碱介导的环状内消旋酸酐的简单且高度对映选择性的
甲醇分解可产生多种二
羧酸单甲酯,其 ee 高达 99%。从这些产品中,可以通过 Curtius 降解相应的酰基
叠氮获得非天然的 N-保护的 β-
氨基酯。随后保护基团的裂解导致游离β-
氨基酸的产率极好。通过外消旋酸酐的对映异构体差异化打开,合成上非常有用的区域异构
氨基酸酯变得容易获得。