1377940-04-9Relevant academic research and scientific papers
Nucleophilicity parameters of enamides and their implications for organocatalytic transformations
Maji, Biplab,Lakhdar, Sami,Mayr, Herbert
supporting information; experimental part, p. 5732 - 5740 (2012/06/01)
The kinetics of the reactions of eleven substituted enamides with benzhydrylium ions (diarylcarbenium ions) were determined in acetonitrile solution. The second-order rate constants follow the correlation log k 2(20°C)=sN(E+N), which allowed us to derive reactivity parameters N and sN. With 4.6N parameters with the previously reported E parameters of typical Michael acceptors, α,β-unsaturated iminium ions, and the chlorinating agent hexachlorocyclohexa-2,4-dienone allowed us to reliably reproduce the experimental rate constants of the reactions with these electrophiles. The reactions of enamides with α,β-unsaturated iminium ions only proceeded in the presence of bases (e.g., 2,6-lutidine), which was explained by the low Lewis acidities of the iminium ions. The consequences of these results for the use of enamides in organocatalytic reactions are discussed. Nucleophile-specific parameters N and sN of enamides allowed a prediction of the rates of their reactions with various electrophiles and enabled a resolution of the mechanism of iminium-activated reactions of α,β-unsaturated aldehydes with enamides (see scheme).
