Heterocumulene-mediated annelation of a [1,3,4]thiadiazine or [1,3,4]oxadiazine ring into an imidazole ring: Preparation and crystal structure of some derivatives of the unknown imidazo[1,5-d]-[1,3,4]thiadiazine and imidazo[1,5-d][1,3,4]oxadiazine ring systems

Article abstract of DOI:10.1016/S0040-4020(01)86770-3

The aza-Wittig reaction of iminophosphorane 2 derived from 1 -amino-3-phenyl-2-thioxo-4-imidazolidinone 1 with heterocumulenes leads to fused imidazoles. Iminophosphorane 2 reacts under mild conditions with isothiocyanates to form imidazo[1,5-d]-[1,3,4]thiadiazines 3 which undergo S-methylation to give imidazo[1,5-d][1,3,4]thiadiazinium salts 4. Iminophosphorane 2 also reacts with isocyanates under mild conditions to give imidazo[1,5-d][1,3,4]oxadiazines 5. The N-aminoheterocycle 1 by the action of diaryl carbodiimides undergoes ring-closure/ring-opening reaction to give the corresponding [1,2,4]triazoles 7, which by sequential treatment with trimethyloxonium tetrafluoroborate and triethylamine/methanol are converted into the oxygen analog 9. The crystal structure of the hydrated salt 4a has been solved by X-Ray diffraction methods. The two independent cations form dimers that pack in chains along the b axis through hydrogen interactions, in such away that all anions and solvent molecules (H₂O and 2 HCCl₃ in the asymmetric unit) are located in the unit cell into two channels which are described.