Selenium-Containing heterocycles from isoselenocyanates: synthesis of 5-Amino-2,4-dihydro-3H-1,2,4-triazole-3-selones

The reaction of S-methylisothiosemicarbazide hydroiodide (= S-methyl hydrazinecarboximidothioate hydroiodide; 1), prepared from thiosemicarbazide by treatment with MeI in EtOH, and aryl isoselenocyanates 5 in CH2Cl2 affords 3H-1,2,4-triazole-3-selone derivatives 7 in good yield (Scheme 2, Table 1). During attempted crystallization, these products undergo an oxidative dimerization to give the corresponding bis(4H-1,2,4-triazol-3-yl) diselenides 11 (Scheme 3). The structure of 11a was established by X-ray crystallography

Selenium-containing heterocycles from isoselenocyanates: synthesis of 2-methylidene-1,3-selenazolidine derivatives

A convenient and unequivocal synthesis of the title compounds from isoselenocyanates, malononitrile or 2-cyanoacetate, and 1,2-dibromoethane or a-halogenated carboxylic acid derivatives is reported. The proposed reaction mechanism involves in situ cyclization of different halogenated compounds with an intermediate keten-N,Se-acetal, generated by the base promoted nucleophilic addition of the acidic cyanomethylenes to aliphatic and aromatic isoselenocyanates. Chemical and spectroscopic evidence for the structures of the new compounds is presented

Selenium-containing heterocycles from Isoselenocyanates: Synthesis of 1,3-Selenazinane and 1,3-Selenazinanone derivatives

The reaction of the intermediate ketene N,Se-hemiacetal 3, prepared from cyanomethylene derivatives 1 by treatment with Et3N and aryl isoselenocyanates 2, with bis-electrophiles 6, 7, 9, and 11 in DMF affords tetrahydro-1H-1,3-selenazine (= 1,3-selenazinane) derivatives 8, 10, and 12 in good yield (Scheme 2 and Tables 1 – 3). Chemical and spectroscopic evidence for the structures of the new compounds are described. The structures of 8d and 12e are established by X-ray crystallography (Figs. 1 and 2)