Identification of the condensation products of 1,2- and 1,3-amino alcohols with keto esters by NMR spectroscopy, mass spectrometry and X-ray crystallography studies. Open or ring forms?

Abstract

The structure of fifteen products of the condensation of 1,2- and 1,3-amino alcohols with different keto esters has been studied in the solid state, in non-polar solution and in the gas phase by X-ray crystallography, nuclear magnetic resonance spectroscopy and mass spectrometry. The 1,3-keto esters gave rise to open-chain products stabilized by a conjugated double-bond system formed through a hydrogen-atom rearrangement from the expected Schiff base. In the gas phase, the ring form was also observed. 1,4- and 1,5-keto esters gave 1,3-oxazolidines and tetrahydro-1,3-oxazines as primary products, which were easily converted into bicyclic lactams. The mass spectral fragmentations of the compounds are discussed in detail.