Cyclisation of novel amino oxo esters to tetramic acids - Density functional theory study of the reaction mechanism

The synthesis of novel N-urethane-protected gamma-methylamino-beta-oxo esters and their use as precursors for the preparation of N-methyltetramic acids is described. The presence of the bulky urethane protecting group on the nitrogen atom gives rise to rotational isomers detectable in the NMR spectra of the compounds, along with the keto/enol tautomerism. The mechanism of the cyclisation reaction of gamma-amino-beta-oxo esters to tetramic acids was studied theoretically by the B3LYP hybrid density functional method. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).