A Flexible Synthetic Approach to Fluorescent Chromeno[4,3‐b]pyridines and Pyrano[3,2‐c]chromenes from Electron‐Deficient 3‐Vinylchromones

Abstract

We report a flexible approach to the synthesis of phenanthrene-like heterocycles through organocatalytic AN-RORC (Addition of the Nucleophile, Ring Opening, and Ring Closure) reaction of electron-deficient 3-vinylchromones with cyanoacetamide. Addition of highly basic DBU (1,8-diazabicyclo [5.4.0]undec-7-ene) or tetramethylguanidine (TMG) at 80°C leads to chromeno [4,3-b]pyridines in good yields, whereas Et 3 N at 20°C made it possible to obtain the less accessible pyrano [3,2-c]chromenes and their 2-imines. The synthesis proceeds in mild conditions (EtOH, 20-80°C), is versatile and applicable for a wide scope of reactants. The obtained compounds show bright fluorescence in the range 460-595 nm with high quantum yields (up to 0.84) in various solvents (MeCN, DMSO, EtOH, H 2 O).

Fluorescent 5H‐Pyrano[3,2‐c]chromenes: Synthesis, Photophysical Properties and Sensing of Nucleophilic Anions

“…All synthesized pyranochromenes 6 a – r are highly fluorescent in the yellow‐green range (Table 2). Previously, very insignificant solvatochromism of 5 H ‐pyranochromenes was noted, [12a] because the solvent in all experiments was only the polar protic i ‐PrOH. This solvent, in addition, did not reduce the fluorescence intensity.…”

“…Based on earlier studies, [12][13][14] we proposed that this reaction begins with a nucleophilic attack of the ester (5) at position 2 of the chromone 1 a. This is accompanied by the opening of the γpyrone system.…”

“…In previous works, [12] we developed a convenient approach to the synthesis of highly fluorescent (Φ rel up to 0.84) nonplanar phenanthrene-like heterocycles -5H-chromeno [4,3b]pyridines 3 and 5H-pyrano[3,2-c]chromenes 4 (Scheme 1, part b). This approach is based on tandem ANRORC reaction of electron-deficient 3-vinylchromones 1 with cyanoacetamide (2).…”

Effect of a Substituent in the Fourth Position on the Optical Properties of 2-Oxonicotinonitriles

“…The pyridone fragment, in particular, the 2-oxonicotinonitrile one, causes the appearance of fluorescent properties in the molecule [25][26][27][28][29][30][31][32][33][34][35][36]. However, there is practically no information in the literature on the systematic study of the effect of an individual substituent on the photophysical properties of such compounds, despite the fact that the optical properties can be finely tuned by introducing individual functional groups.…”