Michael condensation of 2-(4-carboxybenzylidene)-3,4-dihydronaphthalene-1(2H)-one with methylene active compounds in the targeted synthesis of O-heterocyclic hybrid systems

Approaches to the design of new hybrid polyoxaheterocyclic compounds based on the interaction of 2-(4-carboxybenzylidene)-3,4- dihydronaphthalene-1(2H)-one with methylene active compounds of the 2H-chromen-2-one series – 3 -(1,3-dioxobutan-1-yl)-2H-chromen- 2-one and 4-hydroxy-2H-chromen-2-one, as well as their carbocyclic analogue – 1,3-indanedione under various conditions have been considered. It has been revealed for the first time that during the reaction of the studied chalcone with 3-acetoacetyl-2H-chromen-2-one in a piperidine medium, followed by treatment with acetic acid, the hybrid acetate 7-(4-carboxyphenyl)-8-oxo-5,8-dihydro-6H-benzo[h] chromeno[3,2-b]xanthylium is formed. It has been found that the formation of such a hybrid structure with the participation of 1,3-indanedione in the Michael condensation as the methylene component under similar conditions is not possible. In this case, the competitive nucleophilic addition of piperidine at the arylidene fragment with the formation of 4-((1,2,3,4-tetrahydro-1-oxonaphthalen-2-yl)(piperidin- 1-yl)-methyl)benzoic acid is predominant. It has been shown that the condensed adduct of arylidene dihydronaphthalene-1(2H)-one with 1,3-indanedione arises by refluxing the reagents in pyridine. The use of hydrochloric acid in the isolation of the reaction product contributes to the aromatization of the resulting dihydrochromene ring, which ultimately leads to the chloride 7-(4-carboxyphenyl)-8-oxo-6,8-dihydro- 5H-benzo[h]indeno[1,2- b] chromen-13-ilium. A similar trend is observed when 4-hydroxy-2H-chromen-2-one is introduced into the transformation under study. It has been found for the first time that when the reaction is carried out in glacial acetic acid with the addition of piperidine as a catalyst, the latter also acts as an azanucleophile and competitively binds to the reaction center of the substrate. Replacing the solvent with pyridine leads to the formation of a hybrid system, 4-(6-oxo-8,9-dihydro-6H,7H-benzo[h]chromeno[4,3-b]chromen-7-yl)- benzoic acid. In this case, salt formation after treatment with hydrochloric acid is not observed. Thus, in the course of the study, a new synthetic approach to the formation of hybrid chromene, xanthene systems has been considered. The observed salt formation can be the factor in increasing the bioavailability of newly synthesized compounds.