1,3-Dipolar Cycloaddition of Nitrile Imines to 2‑Imino-thiazolo[3,2‑<i>a</i>]pyrimidin-3-ones: Dipole-Initiated Thiazolone-Imidazolone Rearrangement

The 1,3-dipolar cycloaddition of nitrile imines to thiazolo[3,2-a]pyrimidine imines featuring both endocyclic and exocyclic CN bonds was first reported. This reaction resulted in the regio- and stereoselective attachment of two dipole moieties, accompanied by peculiar skeletal rearrangements within the thiazolone fragment. Any products of only dipole addition cannot be isolated. The observed reactivity was explained using DFT protocols to investigate the cyclization mechanism of nitrile imines with thiazolo[3,2-a]pyrimidines.