Imine-tautomers of aminothiazole derivatives: intriguing aspects of chemical reactivities

Abstract

Intriguing reactivities of positional isomers 1-(5-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L 1 ) and 1-(4-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L 2 ) towards environment polluting ions such as mercuric, fluoride, bromide and solvents provide scope to study various self-assemblies formed under different conditions and allied applications. The solid state structures of L 1 and L 2 revealed that both adopt the imine form. However, the number of symmetry independent molecules in asymmetric units as well as the packing patterns of these two compounds have distinguishable features. The asymmetric unit of L 1 has three symmetry non-equivalent molecules. The packing patterns of these two positional isomers differ as L 1 has two arrays of dimeric self-assemblies in contrast to the single array found in the packing of L 2 . The reactivity of L 1 and L 2 with solvents was explored through crystal structure elucidation. The compound L 1 forms solvates with N,N′-dimethylacetamide or dimethylsulphoxide. The structural analysis of solvates of L 1 provided avenues to study conformational adjustments. An unusual example of a metastable solvate of L 1 with N,N′-dimethylacetamide was isolated. A ring-opening reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with L 1 has been observed. The compound L 2 underwent hydrolysis cum bromination with hydrobromic acid in dimethylsulphoxide. The reactivities of L 1 and L 2 towards mercuric and fluoride ions contributed to chemodosimetric signal transductions. The study establishes the impact of subtle changes in structure, reaction and crystallization conditions, which can influence pre-designed crystal engineering.

Conformation and Visual Distinction between Urea and Thiourea Derivatives by an Acetate Ion and a Hexafluorosilicate Cocrystal of the Urea Derivative in the Detection of Water in Dimethylsulfoxide

“…6,7 Certain anion-guiding chemical reactions of thiourea derivatives such as hydrolysis and bromination are useful in anion detection. 8 With the aid of a syn or anti conformer of a thiourea derivative, distinction of acetate and fluoride ions is possible. 9 On the other hand, conformations play an important role in self-assemblies of urea 10−12 and thiourea 13−15 derivatives.…”

Novel Hybrid Compounds Containing Benzofuroxan and Aminothiazole Scaffolds: Synthesis and Evaluation of Their Anticancer Activity

“…Among possible isomers, which can be formed through Pathways 1 and 2 ( Scheme 2 ) both due to the N-1/N-3-oxide equilibrium and/or prototropic tautomerism in the molecule [ 25 , 26 , 27 , 28 ], the most stable one is 3aC ; however, the energy difference between models with different locations of hydrogen (at amine/thiazole N: 3aA / 3aC and 3aB / 3aD ) is less than 1 kcal/mole, suggesting the possible coexistence of both structures ( Table 1 ). The preferable location of the benzofuroxan oxygen moiety is at the N1 atom that is almost by 4 kcal/mol more advantageous compared to the tautomers with an oxygen atom located at N3.…”

“…On the example of the simplest representative of benzofuroxan and aminothiazole hybrids with R=R 2 =R 3 =H 3a, three possible ways have been considered for aromatic nucleophilic substitution reaction: Pathway 1-attack of electrophile on the exocyclic NH 2 , Pathway 2-attack of an electrophile on the endocyclic nitrogen atom and Pathway 3-attack on the carbon atom in Position 5 (Scheme 1). Among possible isomers, which can be formed through Pathways 1 and 2 (Scheme 2) both due to the N-1/N-3-oxide equilibrium and/or prototropic tautomerism in the molecule [25][26][27][28], the most stable one is 3aC; however, the energy difference between models with different locations of hydrogen (at amine/thiazole N: 3aA/3aC and 3aB/3aD) is less than 1 kcal/mole, suggesting the possible coexistence of both structures (Table 1). The preferable location of the benzofuroxan oxygen moiety is at the N1 atom that is almost by 4 kcal/mol more advantageous compared to the tautomers with an oxygen atom located at N3.…”

Nickel(II) complexes with N,O‐donor thiopseudourea ligands: Syntheses, structures, and catalytic applications in Kumada–Corriu cross‐coupling reactions

“…Both HL 1 and HL 2 can have two forms amide and imino‐ketone (Scheme 1) due to amine‐imine tautomerism. [ 17 ] The X‐ray structures revealed that both molecules exist in the imino‐ketone form (Figure 1). The shorter C(8)N(1) bond length compared with the C(8)N(2) bond length indicates the double bond character of the former (Table 2).…”