Recyclization of 5-[Methyl(phenyl)amino]-2-(4-nitrobenzyl)-3-p-tolyl-1,2,4-thiadiazolium Perchlorateinto 9-Methyl-3a-(4-nitrophenyl)-2-p-tolyl-3a,9-dihydrobenzo[b]-lmldazo[4,5-e] [1,4]thiaziee

摘要

Previously was shown that 5-[methyl(phenyl)amino]-3-p-tolyl-2-phenyl-1,2,4-thiadiazolium perchlorates iso-merize under heating into the benzothiazole derivatives.Using the well-known approaches, we synthesized an analog of 1,2,4-tiadiazolium salt containing p-nitrobenzyl substituent in position 2 (transformation I → II) and obtained the corresponding benzothiazole derivatives: salt III and base IV (see the scheme bellow).In DMSO-d6 solution, the compound IV exists as a mixture of stereoisomers in 1:1.3 ratio, as seen from the signals doubling in the ~1H NMR spectrum. This is due obviously to the hindered syn-anti-isomerization at the nitrogen and (or) the hindered rotation around the C-N bond in 1,3-diazadiene fragment. This isomers ratio does not change at raising temperature to 90°C or at replacing the solvent by CDCl3. However, adding trifluoroacetic acid simplifies spectrum: in the region of 2.9 ppm it becomes identical to the spectrum of the salt III.