Synthesis and spectroscopic analysis of substituted 2-aminothiazolines

2-Aminothiazolines can exist in two tautomeric species, amino and imino forms, which can theoretically exist as two stereoisomers. Several methods and techniques have been used to evaluate tautomeric process, but in this case 15N NMR spectroscopy was used due to tautomeric process involves two nitrogen atoms. In this paper, we present the synthesis and a HMBC 1H-15N study of four 2-substituted aminothiazolines. It was observed from HMBC contour plot correlation between five membered ring CH2 groups with sp2 nitrogen around 250 ppm, while aliphatic hydrogen correlates with sp3 nitrogen around 90 ppm, suggesting that amino form is the major or the unique tautomer present in solution. Theoretical calculations at the M06-2X/cc-pVDZ level were performed and indicated that amino tautomer is slightly more stable (∼1 kcal mol−1) than imino one.