Electrochemical fluorination of methyl cinnamates in Et3N · 3HF-MeCN

✍ Scribed by Wojciech Dmowski; Tomasz Kozłowski

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 821 KB
• Volume: 42
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/s0013-4686(96)00185-5

✦ Synopsis

Methyl cinnamates, R-CsH&H~H-COrCH, (R = CHjO, CH3, H, F and CF,), were electrochemically fluorinated in a 1 M solution of (CzH5)jN. 3HF in acetonitrile under potentiostatic conditions. The electrolyses gave, in general, diasteroisomeric mixtures of 2,3-difluoro-3-phenylpropionates (2), 3-acetamido-2-fluoro-3-phenylpropionates

(3) and 2-acetamido-3-fluoro-phenylpropionates (4) as the main products and small amounts of higher fluorinated compounds. The overall chemical yields and current efficiencies were 78-94% and 42-70%, respectively. The substituent R greatly influenced both the chemo-and regioselectivity of fluorination. Ratios of di-and polyfluorinated products to fluoroacetamides and of /?-fluoroacetamides (3) to a-fluoroacetamides (4) have shown reasonable correlation with the resonance substituent constants bp'. The effect of substituent R is discussed in terms of relative stability of intermediate radical-cations. C&addition was the predominant steric outcome of both difluorination and fluoroacetamidation reactions.