Intermolecular cyclization of cinnamoyl isothiocyanate: A new synthetic entry for pyrimidine,triazine, and triazole candidates

An efficient and facile protocol for the synthesis of azine and azole ring systems was reported. Whereas, reaction of cinnamoyl isothiocyanate with N-nucleophile containing compounds (namely, p-aminophenol (2), N¹-phenylbenzene-1,4-diamine (5) and p-aminoacetophenone (8)) tolerated thiourea derivatives 3, 6, and 9, respectively. The later compounds underwent intramolecular cyclization upon treatment with EtONa to give pyrimidinethiones 4, 7, and 10, respectively, in moderate yield (74–79%). Compound 9 underwent intramolecular cyclization and condensation upon reaction with NaOH and benzaldehyde to give pyrimidinethione 12. Thiosemicarbazides 14 and 19 were obtained through reaction of heteroallen 1 with 2,4-dinitrophenylhydrazine 13 and hydrazone 18, respectively. Compound 14 was cyclized to pyrimidinethione 15 and triazine derivatives 17 through its reaction with EtONa at room temperature and refluxing temperature, respectively. Finally, base mediated and oxidative cyclization of thiourea derivative 19 with EtONa, Br₂/AcOH, and Pb(OAc)₂ afforded thiadiazole 20, benzothiazolotriazole 21, and triazolethione 22 derivatives, respectively.