Steric hindrance classified: treatment of isothiocyanatoallene with secondary amines bearing bulky substituents to generate 2-aminothiazoles

Abstract

Twenty secondary amines, bearing two secondary, two tertiary, or a secondary and a tertiary alkyl group or a neopentyl group, were treated with allenyl isothiocyanate to prepare the corresponding 2-dialkylamino-5-methylthiazoles. The relative rates of these reactions, which were strongly dependent on the steric demand of the N-alkyl groups, were measured by using competition experiments and analysis by ¹H NMR spectroscopy. Not only steric, but also some electronic effects on the nucleophilicity of the dialkylamines were discussed.