22038-85-3Relevant articles and documents
19F NMR non-equivalence of diastereomeric amides of 2,2,2-trifluoro-1-phenylethylamine
Wang,Mosher
, p. 987 - 990 (1991)
An alternate synthesis and resolution is reported for 2,2,2-trifluoro-1-phenylethylamine. The 19F NMR of a series of amide derivatives of chiral acids is described. The diastereomeric non-equivalence of the 19F NMR signals (0.05-0.09 ppm) of these amides permits use of these derivatives for determination of enantiomeric purity of alpha-substituted acids. The potential for configurational correlations is discussed.
Bifunctional Thioureas with α-Trifluoromethyl or Methyl Groups: Comparison of Catalytic Performance in Michael Additions
Jiménez, Eddy I.,Vallejo Narváez, Wilmer E.,Román-Chavarría, Carlos A.,Vazquez-Chavez, Josue,Rocha-Rinza, Tomás,Hernández-Rodríguez, Marcos
, p. 7419 - 7431 (2016/09/09)
Thioureas are an important scaffold in organocatalysis because of their ability to form hydrogen bonds that activate substrates and fix them in a defined position, which allows a given reaction to occur. Structures that enhance the acidity of the thiourea are usually used to increase the hydrogen-bonding properties, such as 3,5-bis(trifluoromethyl)phenyl and boronate ureas. Herein, we report the synthesis of bifunctional thioureas with a chiral moiety that include either a trifluoromethyl or methyl group. Their catalytic performance in representative Michael addition reactions was used in an effort to compare the electronic effects of the fluorination at the methyl group. The observed differences concerning yields and ee values cannot be attributed solely to the different steric environments; theoretical results indicate distinct interactions within the corresponding transition states. The calculated transition states show that the fluorinated catalysts have stronger N-H···O and C-H···F hydrogen bonds, while the nonfluorinated systems have C-H···π contacts. These results have shown that a variety of hydrogen-bonding interactions are important in determining the yield and selectivity of thiourea organocatalysis. These details can be further exploited in catalyst design.
Chemoenzymatic dynamic kinetic resolution of α-trifluoromethylated amines: Influence of substitutions on the reversed stereoselectivity
Cheng, Guilin,Xia, Bo,Wu, Qi,Lin, Xianfu
, p. 9820 - 9828 (2013/09/02)
Enzymatic resolution of α-trifluoromethylated amines via kinetic resolution (KR), dynamic kinetic resolution (DKR) employing CALB-Pd/Al 2O3, and a one-pot sequential process of KR/DKR/KR was investigated comparatively for the first time. Although CALB-catalyzed KR of α-trifluoromethylated amines with substituents of methyl (1a), isopropyl (1c), phenyl (1d) and benzyl group (1e) can provide good stereoselectivity factors E from 31 to >200 respectively, DKR and sequential process of KR/DKR/KR possess better practical application potential because of the higher conversion (62%-84%) and the similar enantiomeric excesses (90%-99%). The enantiopreference and inversion for the α-trifluoromethylated amines displayed by CALB were observed and explained by docking modes. Namely, for 1,1,1-trifluoro-2-propylamine (1a), the product amide with R-configuration was obtained, and the enantiopreference was converted to S for the amines (1b-1e) with substituents larger than methyl group. The catalysts recycle, and scale-up experiments were demonstrated successfully. All these results indicated the high efficiency and green feature of this enzymatic process, and its application significance.