ELECTROCHEMICAL FLUORINATION OF METHYL CINNAMATES IN ET(3)N-CENTER-DOT-3HF-MECN

Methyl cinnamates, R-C6H4-CH=CH-CO2CH3 (R=CH3O; CH3, H, F and CF3), we re electrochemically fluorinated in a 1 M solution of (C2H5)(3)N . 3HF in acetonitrile under potentiostatic conditions. The electrolyses gav e, in general, diasteroisomeric mixtures of 2,3-difluoro-3-phenylpropi onates (2), 3-acetamido-2-fluoro-3-phenylpropionates (3) and 2-acetami do-3-fluoro-phenylpropionates (4) as the main products and small amoun ts of higher fluorinated compounds. The overall chemical yields and cu rrent efficiencies were 78-94% and 42-70%, respectively. The substitue nt R greatly influenced both the chemo- and regioselectivity of fluori nation. Ratios of di- and polyfluorinated products to fluoroacetamides and of beta-fluoroacetamides (3) to alpha-fluoroacetamides (4) have s hown reasonable correlation with the resonance substituent constants s igma(p)(+). The effect of substituent R is discussed in terms of relat ive stability of intermediate radical-cations. Cis-addition was the pr edominant steric outcome of both difluorination and fluoroacetamidatio n reactions. Copyright (C) 1996 Elsevier Science Ltd