18534-66-2Relevant academic research and scientific papers
Mechanism of the light-assisted nucleophilic acylation of activated olefins catalyzed by vitamin B12
Walder, Lorenz,Orlinski, Richard
, p. 1606 - 1613 (2008/10/08)
The conjugate addition of acyl groups to C-C double bonds, by a vitamin B12 catalyzed electrochemical reduction of acetic anhydride in the presence of Michael olefins and under visible light, is shown to involve sequential formation and cleavage of the Co-C bond in acetylcobalamin. Photolysis of this intermediate takes place efficiently only in the presence of the activated olefin. The rate constant of acylation of B12s by acetic anhydride (k1 = 0.017 M-1 s-1), the quantum yield of the visible light induced cleavage of the Co-C bond (Φ ≈ 0.35), and the relative rate of acylation of a series of activated olefins were determined electrochemically from catalytic currents. These values are comparable with independently measured k values for the isolated reaction steps. The k values for the acetyl-transfer reaction correlate well with the reduction potentials of the activated olefins or with their σp-, exhibiting a linear free energy relationship (ρ = 2.3). The transferred acyl moiety reacts as a Co-stabilized nucleophilic radical and not as a free radical.
