A divergent and regioselective approach to fused pyridines was developed through formal [3 + 3] cyclocondensations from simple 2,3-unsubstituted chromones or their enaminone precursors.

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A new and efficient domino reaction of 3-chlorochromones with electron-rich aminoheterocycles was developed which allows for a convenient synthesis of a variety of pyrazolo[3,4-b]pyridines, pyrrolo[2,3-b]pyridines, pyrido[2,3-d]pyrimidines and benzofuro[3,2-b]pyridines. The products exhibit strong fluorescence. In addition, they exhibit significant ecto-5'-nucleotidase inhibition properties and cytotoxic behavior.

A new strategy for the synthesis of polycyclic imidazole‐containing N‐heterocycles, based on the two general synthetic ways, namely the Pd(II)‐catalyzed intramolecular arylation via CH/CHal and CH/CH coupling reactions, was developed. The method proposed here enables the synthesis of many fused N‐heterocycles containing purine, 1‐deazapurines and benzimidazole structural units.

Hitherto unknown 3,3'-carbonyl-bis(chromones) 8, dimeric chromones bridged by a carbonyl group, were prepared by reaction of chromone-3-carboxylic acid chloride with 3-(dimethylamino)-1- (2-hydroxyphenyl)-2-propen-1-ones 9. The method is generally applicable for the synthesis of novel symmetrical or non-symmetrical products which were found to inhibit mammalian alkaline phosphatases.

The reaction of electron-rich aminoheterocycles with 1,3-CCC-dielectrophiles, such as 3-formylchromones, acylpyruvates, and chalcone, provided diversely fused pyridines. Starting from 5-amino-1-(2,3-O-isopropylidene-b-D-ribofuranosyl)-1H-pyrazole, nucleosides containing a pyrazolo[3,4-b]pyridine fragment were obtained, which can be considered as adenosine deaminase (ADA) inhibitors.

During the optimization of the conditions of the cyclization, we were able to isolate sideproducts 9 and 10 (Scheme 2). The quantity of these compounds strongly depends on the conditions (see legend of Table 2). The formation of products 9 can be explained by reaction of 6 with two molecules of the amine, i.e. conjugate addition to the ynone and nucleophilic substitution at the arene. Products 10 are formed by conjugate addition of the amine to the alkynone moiety. Under the standard conditions applied for the synthesis of quinolones 7, sideproducts 9 and 10 were formed only in very small quantities (1-2%). However, 9a-d could be isolated and spectroscopically characterized when the reaction was carried out at lower temperature. Reduction of the reaction time during the synthesis of nitroquinolone derivatives allowed us to isolate intermediates 10a and 10b. In general, the yields of unwanted side-products 9 and 10 increased when potassium fluoride was employed instead of standard K 2 CO 3 and K 3 PO 4 . Scheme 2. Side-products 9 and 10. Yields of isolated compounds obtained in reaction conditions specified in footnotes g, h, and i of Table 2.

A series of new heteroannulated pyrido[2,3‐c]coumarins have been prepared by the domino reactions of chromone‐3‐carboxylic acid derivatives with electron‐rich binucleophilic aminoheterocycles. The products contain the core structures of coumarin, pyridine, and an annulated five‐membered heterocyclic system, namely pyrazole, pyrrole, or isoazole. The fluorescence of the products was investigated. The products inhibit ecto‐5′‐nucleotidase (e5′NT) enzymatic activity.