2-(3-acylselenoureido)Benzonitriles and 2-(3-acylselenoureido) thiophene-3-carbonitriles. Preparation, structure elucidation, cyclization and retrocyclization reactions

Synthesis of 2-(3-acylselenoureido)benzonitriles and 2-(3-acylselenoureido) thiophene-3-carbonitriles 5a-5f by addition of 2-aminonitriles 4a-4c to ben zoyl- or 2,2-dimethyl-propanoylisoselenocyanate and their cycloaddition rea ctions are described. Structures of compounds 5a-5f were supported by CIMS, FTIR, H-1, C-13, Se-77 and N-15 NMR spectra. The parameters of N-15 and Se -77 nuclei were obtained from inverse H-1-X 2D HMBC and GSQMBC correlation experiments at natural abundance. Structure of compound 5b was confirmed by X-ray analysis. The geometry of 5b was optimized by nb initio RHF/DZVP qua ntum chemistry calculation. A very good correlation between the calculation and experimental data was found. The geometry of 5e was optimized by nh in itio DFT/VWN/DZVP quantum chemistry calculation. It was found that title co mpounds 5a-5f do not undergo isomerization to acylisoselenoureas, in contra st to analogous ester derivatives. Fused 6-imino-6H-1,3-selenazinium salts (chlorides 6a-6f, hydrogensulfates 7a-7f and tetrafluoroborates 8a-8f) were prepared by an acid cyclization of 5a-5f. It was found that neutralization of 6a-6f, 7a-7f and 8a-8f led to their retrocyclization to 5a-5f. Selenour eas 5a-5f with equimolar amounts of methanolic potassium hydroxide afforded potassium salts 9a-9f. Only the salts 9b, 9c, 9e and 9f of the thiophene s eries were isolated. Their heating in methanol solution led to deacylation of isoselenoureas 10b and 10c. The bl situ prepared compounds 9a and 9d cyc lized and deacylated to 4-aminoquinazoline-2-selenole 11a under the same co nditions. The compounds 5a-5f and 10a-10c cyclized to fused 4-aminopyrimidi ne-2-selenols 11a, 11b and 4-aminopyrimidine-2-selenone 12c by boiling in m ethanolic potassium hydroxide solution.