Isothiazolium salts 2 and 3 are easily available by reaction of (Z/E)-beta-thiocyanatovinyl aldehydes with primary aliphatic and aromatic amines in acetic acid or with aromatic amine hydrochlorides, respectively. Preparative advantages of this reaction are demonstrated and discussed. Reaction of 3 with secondary amines results in an unexpected formation of 6a-lambda-4-thia-1,6-diazapentalenes 5, a new typ of thiadiazapentalenes anellated with a heterocyclic ring system. The structure of 5 was evidenced by IR, UV, H-1-, C-13-n.m.r. spectral data and supported by elemental analysis. By means of N-15- and C-13-n.m.r. spectroscopy the synthesized thiadiazapentalenes were found to be stable towards protonation.
Muehlstaedt,M. et al., Journal fur praktische Chemie (Leipzig 1954), 1976, vol. 318, p. 507 - 514