化学
非对映体
位阻效应
试剂
氟
化学位移
立体化学
氟-19核磁共振
有机化学
药物化学
核磁共振波谱
物理化学
作者
Yoshio Takéuchi,Hironobu Ogura,Yohko Ishii,Toru Koizumi
出处
期刊:Chemical & Pharmaceutical Bulletin
[Pharmaceutical Society of Japan]
日期:1990-01-01
卷期号:38 (9): 2404-2408
被引量:16
摘要
As a part of our work on synthetic studies of chiral monofluoro compounds and molecular design of efficient reagents for optical purity determination, we focused on novel α, α-disubstituted α-fluoroacetic acids (8a-d) (R1=Me, Ph; R2=C≡CPh, Me, Bu). The ethyl esters (13a-d) were prepared by introduction of alkyl groups into the appropriate α-keto acids (9a, b) followed by fluorination of the corresponding hydroxy-esters (12a-d) with diethylaminosulfur trifluoride (DAST). For comparison with Mosher's reagent (2-methoxy-2-trifluoromethylphenylacetic acid, (MTPA)), the ethyl esters (13a-d) were converted into three representative diastereoisomers, (14a-d), (15a-d), and (16a-d), and 19F-nuclear magnetic resonance (19F-NMR) chemical shift differences between pairs of diastereoisomers (Δδ) were obtained. These α, α-disubstituted α-fluoroacetate derivatives have much larger Δδ values than the corresponding derivatives of MTPA, which strongly indicates that the acids (8a-d) can potentially be better reagents for ee determination than MTPA. The influence on the Δδ values of the steric effects which arise upon introduction of the two substituents (R1 and R2) on the fluorine-bearing chiral center is also discussed.
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