Oxidative Cyclization of 5H-Chromeno[2,3-b]pyridines to Benzo[b]chromeno[4,3,2-de][1,6]naphthyridines, Their NMR Study and Computer Evaluation as Material for LED

Abstract

Oxidative cyclization is one of the most significant reactions in organic synthesis. Naphthyridine derivatives are often used as luminescence materials in molecular recognition because of their rigid planar structure and as new drugs. Organic light-emitting diodes (OLEDs) have rapidly grown as one of the leading technologies for full-color display panels and eco-friendly lighting sources. In this work, we propose the synthesis of previously unknown benzo[b]chromeno[4,3,2-de][1,6]naphthyridines via intermolecular oxidative cyclization of 5-(2-hydroxy-6-oxocyclohexyl)-5H-chromeno[2,3-b]pyridines in formic acid. The investigation of the reaction mechanism using 1H-NMR monitoring made it possible to confirm the proposed mechanism of the transformation. The structure of synthesized benzo[b]chromeno[4,3,2-de][1,6]naphthyridines was confirmed by 2D-NMR spectroscopy. Such a rigid geometry of synthesized compounds is desired to minimize non-radiative energy losses in OLEDs. The quantum chemical calculations are also presented in the study.

Synthesis of novel chromeno[1,6]naphthyridine derivatives in PEG-400 via catalyst-free, one-pot, and multicomponent reactions

“…Recently, Elinson et al reported the synthesis of benzo[ b ]chromeno[4,3,2-de][1,6]naphthyridines via an intermolecular oxidative cyclization of 5-(2-hydroxy-6-oxocyclohexyl)-5H-chromeno[2,3- b ]pyridines in formic acid. 15…”

“…14 Recently, Elinson et al reported the synthesis of benzo[b] chromeno [4,3,2-de][1,6]naphthyridines via an intermolecular oxidative cyclization of 5-(2-hydroxy-6-oxocyclohexyl)-5H-chromeno [2,3-b] pyridines in formic acid. 15 In this line of research and in continuation of our research on the synthesis of novel heterocycles, 16 herein, we report an efficient method for the synthesis of chromeno [1,6]naphthyridine derivatives via a one-pot, three-component condensation reaction between salicylaldehyde derivatives, malononitrile dimer, and active methylene group compounds (5-amino-3-(cyanomethyl)-1H-pyrazole-4carbonitrile/5-amino-3-(cyanomethyl)isoxazole-4 carbonitrile/2-(cyanomethyl) pyrazolo [1,5-a]pyrimidine-3-carbonitrile derivatives/ malononitrile dimer/alkyl malonates) in polyethylene glycol-400 (PEG-400) at 80 1C (Scheme 1). This new nominally catalyst-free pathway provided more than 30 previously (to the best of our knowledge) undescribed chromeno [1,6]naphthyridine derivatives with acceptable yields in PEG-400, which appeared to play a dual role of solvent and catalyst.…”

Thermal Rearrangement of 5-(2-Hydroxy-6-oxocyclohexyl)-5H-chromeno[2,3-b]pyridines

“…However, publications about these are scarce. Among them are ones about rearrangement [ 31 ] and cyclization [ 32 ].…”