Reactions of Ethyl 3-(4-Oxo-4H-chromen-3-yl)prop-2-enoates with 1,2-Binucleophiles

Synthesis of β-vinyl-substituted 4H-chromenes and [4+2] cycloaddition reactions involving them

Based on six representatives of 2-oxonicotinonitriles, the effect of the nature of the substituent in the fourth position of the pyridine system on the photophysical characteristics was studied. The role of the donor/acceptor nature of the substituent and the solvent nature in the absorbing and fluorescent properties of the compounds was shown. 

/pdf/effect-of-a-substituent-in-the-fourth-position-on-the-qge515xi.pdf

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

We report a flexible approach to the synthesis of phenanthrene-like heterocycles through organocatalytic ANRORC (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 Et3 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, H2 O).

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

AIEgens represent a special class of molecules, which are emissive in aggregated state, but show almost no fluorescence in dissolved form. Herein we report on the aggregation-induced emission properties of scandium complex with 2-naphtoyltrifluoroacetone ([Sc(NTA)3]). Fluorescence quantum yield of the complex increases ∼68 times, from 0.005 to 0.34, in aqueous solution by comparison with solution in dimethylformamide. This scandium complex is also emissive in powder form or as a film on a glass substrate, indicating that restriction of intramolecular motions facilitates complex fluorescence. The sensitized fluorescence of rhodamine 6 G and rhodamine B was observed in mixed aggregates of complexes and dyes showing the possibility to use [Sc(NTA)3] as efficient energy donor.

Maxim N. Krivchun

Papers

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

Aggregation-induced emission of scandium complexes with 2-naphtoyltrifluoroacetone