Unusual amino acids III. Asymmetric synthesis of 3-arylalanines
摘要:
21 (Z)-alpha-N-benzoylamino-beta-arylacrylic acids and their esters were prepared by known procedures and hydrogenated to the corresponding optically active alpha-benzoyl-beta-arylalanine derivatives with optical yields in the range of 82-95% ee using the cationic rhodium complex of ''PROPRAPHOS'' as the chiral catalyst No electronical influences of the substituents at the aryl moiety on the enantioselectivity were observed but a sterical one, proved by X-ray crystallographic analysis and computer-aided modellings. Deacylation of the hydrogenated spezies produced the hydrochlorides of the 3-arylalanines attended by a partial racemisation In this case the hydrogenation of urethane type protected dehydroaminoacid derivatives seems to be the alternative.
Dynamic Kinetic Resolution of Azlactones by Bifunctional Thioureas with α‑Trifluoromethyl or Methyl Groups
作者:Marcos Hernández-Rodríguez、Eddy I. Jiménez、Margarita Cantú-Reyes、Miguel Flores-Ramos、Carlos A. Román-Chavarría、Howard Díaz-Salazar
DOI:10.1055/a-1892-9911
日期:2022.10
The asymmetric ring opening of azlactones via dynamickineticresolution (DKR) is investigated by contrasting thioureas incorporating 1-arylethyl substituents against their more acidic trifluoromethylated analogs. All the catalysts under study outperform Takemoto’s thiourea because of the inclusion of an additional chiral center. However, the difference in yield and selectivity between the fluorinated