Asymmetric Synthesis of 2-(α-Aminoalkyl)oxazoles, 2-Oxazolylpyrrolidines, 2-Oxazolylpiperidines: Total Synthesis of 4,5-Dihydroxypipecolinic Acid
作者:Marion Thieme、Eric Vieira、Jürgen Liebscher
DOI:10.1055/s-2000-8719
日期:——
Asymmetric α-alkylation of 2-aminomethyl-4,5-diphenyloxazole was achieved by formation of azomethines 1 and ent-1 with the enantiomers of 2-hydroxypinan-3-one as chiral auxiliaries, reaction with alkylating reagents and final removal of the chiral auxiliary giving rise to optically active 2-(α-aminoalkyl)oxazoles 3, ent-3, 6 and 9. If α,Ï-dihaloalkanes were used the resulting alkylation products could be further cyclized by intramolecular alkylation of the amino group to afford optically active 2-oxazolyl-N-heterocycles 4, ent-4, 7 and 10. The latter could be used for the total synthesis of naturally occurring 4,5-dihydroxypipecolinic acid 13.
以 2-羟基蒎烷-3-酮的对映体作为手性助剂,生成偶氮甲烷 1 和 ent-1,与烷基化试剂反应,最后去除手性助剂,得到光学活性 2-(δ-氨基烷基)噁唑 3、ent-3、6 和 9,从而实现了 2-氨基甲基-4,5-二苯基噁唑的不对称δ-烷基化。如果使用δ,Ï-二卤代烃,所得到的烷基化产物可通过氨基的分子内烷基化进一步环化,得到光学活性的 2-噁唑基-N-杂环 4、ent-4、7 和 10。后者可用于天然 4,5-二羟基哌啶酸 13 的全合成。