ChemInform Abstract: Cyclization Reaction of 1,4‐Disubstituted Thiosemicarbazides. Part 1

The Electronic Structure of the Nitrogen Atoms of Allyl (5- pyridin-2-yl-[1,3,4]-thiadiazol-2-yl)-amine

“…Earlier 100 MHz 1 H-NMR studies in the solution of 1-acyl-(aroyl-)-4-(3-phenylallyl)-thiosemicarbazides [3] and N 1 -[(3-phenylallyl)-thiocarbamyl]amidrazones [4] as well as of the products obtained of the result of the acid cyclization of the linear compounds [5,6] confirmed various tautomeric structures for the above mentioned compounds and the transformation products. Allyl-(1) and 3-phenylallyl-(5-pyridin-2-yl- [1,3,4]thiadiazol-2-yl)-amine (2) [6,7], another product of the acid cyclization of the linear N 1 -[ allyl-(3-phenylallyl)-thiocarbamyl]-amidrazone compounds, turned out to be suitable to study the tautomeric transformations. 19 20 21 b a 13 On account of the allyl-and pyridyl-substituents in the molecule, the exo-and endocyclic nitrogen atoms of 1,3,4-thiadiazole and pyridine rings may appear as amino-, pyrrole-or pyridinetype nitrogens.…”

“…The tautomeric equilibrium is influenced by the exocyclic N6 and C5 substituents on the 1,3,4-thiadiazole ring [1,2]. 2-Amino- [1,3,4]-thiadiazole exists in the amino form in solution and in the solid state. The same tautomer is the main form in 5-alkoxy derivatives.…”

“…In the case of a 2-hydrazino substituent the hydrogen atom also appears at the exocyclic N6 nitrogen atom, but in the sulfonamido group the tautomeric equilibrium shifts towards the imino form (type b, Figure 1). It therefore appeared of interest to examine the tautomeric equilibrium of (5-pyridin-2-yl- [1,3,4] thiadiazol-2-yl)-amine derivatives bearing allyl-and (3-phenylallyl)-substituents (compounds 1 and 2, respectively). Earlier 100 MHz 1 H-NMR studies in the solution of 1-acyl-(aroyl-)-4-(3-phenylallyl)-thiosemicarbazides [3] and N 1 -[(3-phenylallyl)-thiocarbamyl]amidrazones [4] as well as of the products obtained of the result of the acid cyclization of the linear compounds [5,6] confirmed various tautomeric structures for the above mentioned compounds and the transformation products.…”

“…It therefore appeared of interest to examine the tautomeric equilibrium of (5-pyridin-2-yl- [1,3,4] thiadiazol-2-yl)-amine derivatives bearing allyl-and (3-phenylallyl)-substituents (compounds 1 and 2, respectively). Earlier 100 MHz 1 H-NMR studies in the solution of 1-acyl-(aroyl-)-4-(3-phenylallyl)-thiosemicarbazides [3] and N 1 -[(3-phenylallyl)-thiocarbamyl]amidrazones [4] as well as of the products obtained of the result of the acid cyclization of the linear compounds [5,6] confirmed various tautomeric structures for the above mentioned compounds and the transformation products. Allyl-(1) and 3-phenylallyl-(5-pyridin-2-yl- [1,3,4]thiadiazol-2-yl)-amine (2) [6,7], another product of the acid cyclization of the linear N 1 -[ allyl-(3-phenylallyl)-thiocarbamyl]-amidrazone compounds, turned out to be suitable to study the tautomeric transformations.…”

“…19 20 21 b a 13 On account of the allyl-and pyridyl-substituents in the molecule, the exo-and endocyclic nitrogen atoms of 1,3,4-thiadiazole and pyridine rings may appear as amino-, pyrrole-or pyridinetype nitrogens. Consequently, allyl-(1) and 3-phenylallyl-(5-pyridin-2-yl- [1,3,4] 2) [6][7][8][9]. The intensities of the signals prove the interconversion between these tautomeric forms.…”