N,N-disubstituted 2-aminothiazole-5-carboxylates: preparation and rotation of functional groups
A series of new alkyl N,N-disubstituted 2-aminothiazole-5-carboxylates was prepared by condensing α-bromo-β-oxo-esters with N,N-disubstituted thioureas. The products exhibit i.r. carbonyl doublets, the higher and lower wavenumber components arising from the carbonyl O,S-syn-s-trans and anti-s-trans rotamers respectively. Variable temperature 1H n.m.r. examination showed that the barriers to rotation of the 2-amino-groups are in the range 41–47 kJ mol–1. Further evidence for rotational isomerism of the carboxylate group was provided by 13C n.m.r. study, but the size of its rotational barrier could not be assessed.
The spectrometric work shows that there is strong mesomeric interaction between the carboxylate and amine groups.