Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

Characteristics of 2-chloropyridine and thiourea condensation. Structure of the as-formed products and their effect on coating properties during electrochemical nickel plating

The synthesis and spectral characterisation of 2-pyridylisothiuronium chloride were performed by regulating the rate of feeding 2-chloropyridine into a thiourea solution in ethyl alcohol for ensuring its low concentration in the reaction zone. According to the data of NMR spectroscopy (1H,13С,15N), the obtained compound represents an approximately equimolar mixture of two tautomers: the expected isothiuronium salt and pyridinium chloride with an isothiocarbamide substituting group in the 2nd position. The ability of isothiuronium salt to transit tautomerically to pyridinium salt is determined by the presence of two main centres, including nitrogen atoms of the isothiourea unit and a nitrogen atom of the pyridine ring. A quantum chemical analysis performed using the DFT method showed that the free energy values of the tautomers were similar, with the tautomer protonated on the nitrogen imido-atom being 2.9 (in the gas phase) and 4.7 kcal/mole (taking into account the dimethyl sulphoxide solvent DMSO at the PCM level) more advantageous as compared to the pyridinium salt. A small difference in the tautomer energies determines their formation in an approximately equimolar quantity. A rapid addition (5–10 mL/min) of 2-chloropyridine to the thiourea solution in the reaction zone creates the surplus of the reagent, acting as a base and causing splitting of the isotiuronium salt. This leads to an additional formation of bis(2-pyridyl)sulphide in the reaction medium, representing a valuable ligand for obtaining coordination compounds. The synthesised mixture of tautomers was examined as an additive to the standard nickel-plating electrolyte. In the concentration of 0.3–0.5 g/L, this additive ensured the production of bright low-porous nickel coatings at a sufficiently high current density of 5–10 A/dm2 and a current yield of 98–99 %.