ONSH: optimization of oxidative alkylamination reactions through study of the reaction mechanism

Oxidative alkylamination of electron-deficient (hetero)aromatic compounds, via the nucleophilic substitution of hydrogen, is a methodology that has made significant progress since the introduction of AgPy(2)MnO(4) as oxidant. This oxidant generally gives good conversions and yields, whereas the use of KMnO(4) only sometimes works equally well. In order to rationalize this, the reaction mechanism of oxidative alkylamination has been studied. 3-Nitropyridine (1), 1,3-dinitrobenzene (2), and quinazoline (3) were chosen as model substrates and n-butylamine and pyrrolidine as model alkylamines. The rate-limiting step of the mechanism for these substrate/alkylamine combinations was determined. With the use of (1)H NMR spectroscopy thermodynamic properties of sigma(Eta)-adduct formation were deduced and the effect of additives on the adduct formation was investigated. The fundamental insights resulting from these studies led to the identification of a cheap additive (tetrabutylammonium chloride), which in combination with the standard and cheap oxidant KMnO(4) generally gave excellent yields, similar to the ones previously obtained with more expensive AgPy(2)MnO(4).