A new approach to the synthesis of selected quinolinecarbaldehydes with carbonyl groups located at C5 and/or in C7 positions is presented in this paper in conjunction with spectroscopic characterization of the products. The classical Reimer-Tiemann, Vilsmeier-Haack and Duff aldehyde synthesis methods were compared due to their importance. Computational studies were carried out to explain the preferred selectivity of the presented formylation transformations. A carbene insertion reaction based on Reimer-Tiemann methodology is presented for making 7-bromo-8-hydroxyquinoline-5-carbaldehyde. Additionally, Duff and Vilsmeier-Haack reactions were used in the double formylation of quinoline derivatives and their analogues benzo[h]quinolin-10-ol, 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde, 8-(dimethylamino) quinoline-5,7-dicarbaldehyde and 10-hydroxybenzo[h]quinoline-7,9-dicarbaldehyde. Four Schiff base derivatives of 2,6-diisopropylbenzenamine were prepared from selected quinoline-5-carbaldehydes and quinoline-7-carbaldehyde by an efficient synthesis protocol. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, FTIR, electronic absorption spectroscopy and multinuclear NMR. The electrochemical properties of 8-hydroxy-quinoline-5-carbaldehyde, 6-(dimethylamino)quinoline-5-carbaldehyde and its methylated derivative were investigated, and a strong correlation between the chemical structure and obtained reduction and oxidation potentials was found. The presence of a methyl group facilitates oxidation. In contrast, the reduction potential of methylated compounds was more negative comparing to non-methylated structure. Calculations of frontier molecular orbitals supported the finding. The structures of 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde and four Schiff bases were determined by single-crystal X-ray diffraction measurements.

New approaches to the synthesis of 4,7-dichloro-1,10-phenanthrolines and their corresponding 9H-carbazol-9-yl-, 10H-phenothiazin-10-yl- and pyrrolidin-1-yl derivatives were developed. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, electronic absorption spectroscopy and multinuclear NMR in both solution and solid state including ¹⁵N CP/MAS NMR. The structures of 5-fluoro-2,9-dimethyl-4,7-di(pyrrolidin-1-yl)-1,10-phenanthroline (5d), 4,7-di(9H-carbazol-9-yl)-9-oxo-9,10-dihydro-1,10-phenanthroline-5-carbonitrile (6a) and 4,7-di(10H-phenothiazin-10-yl)-1,10-phenanthroline-5-carbonitrile (6b) were determined by single-crystal X-ray diffraction measurements. The nucleophilic substitutions of hydrogen followed by oxidation produced compounds 6a and 6b. The electrochemical properties of selected 1,10-phenanthrolines were investigated using cyclic voltammetry and compared with commercially available reference 1,10-phenanthrolin-5-amine (5l). The spatial distribution of frontier molecular orbitals of the selected compounds has been calculated by density functional theory (DFT). It was shown that potentials of reduction and oxidation were in consistence with the level of HOMO and LUMO energies.

Complexes of 1,10‐phenanthrolines with cations of transition metals have broad range of applications. This work aims at designing and investigating phenothiazine and carbazole substituted 1,10‐phenanthrolines as ligands for future complexes with transient metal cations. The combined electrochemical, spectroelectrochemical and DFT studies were employed to demonstrate the effect of broken symmetry in substituted 4,7‐di(phenothiazine)‐1,10‐phenanthrolines on their spectroelectrochemical properties. A reversible color change (new absorption band around 500 nm) due to phenothiazine radical cation was observed in the first oxidation step. Results further indicate that phenothiazine substituents behave as two equivalent but almost electronically isolated redox centres. The work additionally presents a comprehensive reaction mechanistic study of oxidation and reduction processes complemented by HPLC‐MS/MS identification.

Water-soluble ligands based on a 1,10-phenanthroline core are relatively poorly studied compounds. Developing efficient and convenient syntheses of them would result in new interesting applications because of the importance of 1,10-phenanthrolines. In this manuscript, we describe novel and practical ways to introduce a carboxyl and, for the first time, a phenol and dithiocarboxyl group under mild reaction conditions. This strategy enables highly efficient and practical synthesis of suitable organosulfur compounds with high added value, high chemoselectivity, and a broad substrate range. We present the selective conversion of a hydroxydialdehyde in the form of 10-hydroxybenzo[h]quinoline-7,9-dicarbaldehyde into its derivative, unique hydroxydicarboxylic acid, by an oxidation procedure, giving 10-hydroxybenzo[h]quinoline-7,9-dicarboxylic acid. A similar procedure resulted in the formation of 9-methyl-1,10-phenanthroline-2-carboxylic acid by oxidation of commercially available neocuproine. An alternative method of obtaining 1,10-phenanthroline derivatives possessing carboxylic acid group can be based on the hydrolysis of ester or nitrile groups; however, this synthesis leads to unexpected products. Moreover, we apply Perkin condensation to synthesize a vinyl (or styryl) analog of 1,10-phenanthroline derivatives with phenol function. This reaction also demonstrates a new, simple, and efficient strategy for converting methyl derivatives of 1,10-phenanthroline. We anticipate that the new way of converting methyl will find wide application in chemical synthesis.