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Reactions of 7-hydroxy-2-methyl-8-formylisoflavone with 4-chloromethylcoumarins synthesized 8-(coumarin-4-yl)furo[2,3-h]chromones, which reacted with 2-bromoacetylbenzofuran to produce 8-(benzofuroyl)furo [2,3-h]chromone. Recyclization of the corresponding furochromones through the action of hydrazine hydrate gave 4-hydroxybenzofurans with pyrazole and coumarin or benzofuroyl substituents.

7-Hydroxy-8-methyl-4'-methoxy-6-formylisoflavone was synthesized from the 6-aminomethyl derivative of 7-hydroxychromone under modified Duff reaction conditions and underwent heterocyclization to form linear furo- and pyranochromones.

This mini-review for the first time summarizes and systematizes all the data available in the literature on the synthesis and properties of 3-thienyl/benzothienylchromones, starting from 1960. Two main approaches to the formation of target structures are presented. The conditions of cyclization reactions, oxidative rearrangement, transition metals catalyzed CH activation and annulation reactions, etc. are discussed. Testing data for some types of biological activity of a number of the 3-thienyl/benzothienylchromones and the products of their transformation into the pyrazole cycle are given.

An effective approach to the synthesis of the first examples of novel ring systems 11H-chromeno[3',2':3,4]pyrrolo[2,1-b][1,3]thiazol-11-one and 13H-chromeno[3',2':3.4]pyrrolo[2,1-b][1,3]benzothiazol-13-one via intramolecular cyclization of 3-[1,3-(benzo)thiazol-2-yl]-2-chloromethylchromones has been developed.

Reaction features of polyhydroxydeoxybenzoins and their heteroatomic analogs with succinic and glutaric anhydrides were studied and shown to be useful for synthesizing 3-(3-pyrazolyl)butyric acids and 4,11-dioxo-8,10,11,12-tetrahydro-4H,9H-pyrano[2,3-a]xanthene derivatives with a butyric acid moiety.

The present review represented the advanced synthetic strategies for chromones annulated at the C(7)-C(8) bond with five-membered, six-membered, and seven-membered oxygen-containing heterocycles with two heteroatoms, such as 6 H -[1,3]dioxolo[4,5- h ]chromen-6-one, 2,3-dihydro-7 H -[1,4]dioxino[2,3- h ]chromen-7-one, 3,4-dihydro-2 H ,8 H -[1,4]dioxepino[2,3- h ]chromen-8-one, 2,3-dihydro-1 H ,7 H -chromeno[7,8-b][1,4]oxazin-7-one, 4 H ,12 H -pyrano[2,3-a]phenoxazine-4-one and 9,10-dihydro-4 H ,8 H -chromeno[8,7-e][1,3]oxazin-4-one. The biological activity of naturally occurring and modified synthetic fused hetarenochromones has been also highlighted.

Furo[2,3-h]chromone and pyrano[2′,3′:5,6]chromeno[4,3-b]pyridine derivatives were synthesized from 7-hydroxy-8-formylisoflavones, which were prepared from natural isoflavones using a Duff reaction, via reactions with bromoacetophenones and ethyl 3-aminocrotonate, respectively.

6-(2-Methylthiazol-4-yl)-4-methylumbelliferone derivatives were synthesized from 4-(1,3-thiazol-4-yl)-1,3-benzenediols via a Pechmann reaction and were modified by acylation and aminomethylation.

A two-step synthesis of 6-(5-isoxazolyl)coumarins was developed. Recyclization of 7-hydroxychromones by hydroxylamine into 4-(5-isoxazolyl)-1,3-benzenediols followed by condensation with acetoacetic ester produced 6-(5-isoxazolyl)-4-methylumbelliferone derivatives with aryl and hetaryl substituents on the isoxazole ring.

Articles reporting on the chemical modifications and transformations of 3-azahetarylchroman-4-ones are rewieved. The following 3-azahetarylchroman-4-ones’ transformation - reduction of 3-azahetarylchromon-4-ones to the corresponding 3-azahetarylchromanols, -chromenes, and -3,4-dihydrochromenes, alkylation of 3-azahetarylchromanols, reconversion into 3-azahetarylchromones, formation of 3-hetarylchroman-4-one oximes and corresponding oxime ethers, recyclization into 3-aryl-4-hetarylpyrazolines are described. The biological activity of 3-azahetarylchroman-4-one modification or transformation products are also adduced.

A two-step synthesis of 6-(3-pyrazolyl)coumarins starting from 7-hydroxy(acetoxy)chromones was developed. It included their recyclization using hydrazine hydrate into 4-(3-pyrazolyl)-1,3-benzenediols followed by condensation with acetoacetic ester to produce 6-(3-pyrazolyl)-4-methylumbelliferone derivatives with aryl, aryloxy, and hetaryl substituents on the pyrazole ring.

Articles reporting on the synthesis and biological activity of 3-hetarylchroman-4-ones are reviewed. The following preparative methods to 3-hetarylchroman-4-ones - nucleophilic substitution in 3-bromochroman-4-ones, cyclization of 2-hydroxy-α-hetarylacetophenones, reduction/hydrogenation of 3-azahetarylchromones, their benefits and disadvantages are described. The biological activity of 3-hetarylchromanones is also surveyed.

The propensity of cyclic carboxylic anhydrides to undergo ring-opening was exploited in a reaction with 2'-hydroxy-α-heteroarylacetophenones leading to the formation of chromones. New simple method was developed for the synthesis of 2-(ω-carboxyalkyl)-3-heteroarylchromones without protecting either the phenolic or the carboxylic groups. Treatment with hydrazine led to the formation of 3(5)-(ω-carboxyalkyl)-5(3)-(2,4-dihydroxyphenyl)-4-heteroarylpyrazoles.

Amination of 6-alkyl-2-chloromethyl-7-hydroxy-3-(4-methylthiazol-2-yl)-4H-chromen-4-ones by secon-dary cyclic amines gives the corresponding 2-dialkylaminomethyl derivatives.

The interaction has been studied of a series of substituted 3-hetaryl-7-hydroxychromones with amino acids and formaldehyde (reactants ratio 1: 1: 2 respectively). In the case of glycine and Het = 3-isoxazolyl the product of aminomethylation at position 8 of the chromone was obtained, and with other Het (including Het = 4-phenyl-1,2,4-triazol-3-yl) 2-[6-alkyl-3-hetaryl-4-oxo-9,10-dihydro-4H,8H-chromeno[8,7-e][1,3]-oxazin-9-yl]acetic acids were formed. With β-alanine and Het = 4-phenyl-1,2,4-triazol-3-yl the corresponding β-substituted propionic acid was synthesized, but proline did not participate in the reaction, leading to bis(6-ethyl-3-hetaryl-7-hydroxychromon-8-yl)methane.

Chromones of type (III) or (VII) are prepared by the reaction of acetophenone derivatives of type (I) with cyclic carboxylic anhydrides.

Potential biologically active title compounds of type (VI) are prepared by amination of hydroxychromone (IV) with secondary cyclic amines (V).

Homologous and isomeric series of thiazole derivatives of isoflavones were produced on the basis of α-(4-methyl-2-thiazolyl)-2-hydroxyacetophenones. A study of α-(4-methyl-2-thiazoyl)-2-hydroxyacetophenones by PMR spectroscopy showed that these compounds exist in most nonpolar and low polarity organic solvents exclusively in the ketone form, but in dimethyl sulfoxide solution both the ketone and enol forms are observed in various ratios. A simple and effective preparative method of synthesis of homologs of 3-(2-diazolyl)-chromones was developed, and their alkylation at the phenolic hydroxyl was studied. Data of biological tests of the compounds synthesized are presented.

For unknown reasons, the cyclization of title acetophenones proceeds only in the presence of thiazole rings.

The reaction of a-(2-benzthiazolyl)-2, 4-dihydroxy-5-alkylacetophenones with anhydrides and chlorides of carboxylic acids yielded 3-(2-benzthiazolyl)chromones with electron-acceptor and electron-donor substituents, as well as chromones unsubstituted in the 2 -position. Their acylation, alkylation, and aminoacylation reactions and their interaction with electrophilic and nucleophilic reagents were studied.

Isoxazole analogs of isoflavones have been synthesized by the cyclization of α-(3-isoxazolyl)-2-hydroxyacetophenones. Their alkylation, acylation, and electrophilic substitution reactions, and reactions with binucleophiles have been studied. 3-(3-Isoxazolyl)-7-methoxychromones are rearranged selectively into 2-aminochromone derivatives by the action of hydroxylamine as a result of a double recyclization and are recyclized into pyrazole derivatives by hydrazine. Preparations with hypolipidemic, anabolic, hypoglycemic, and antiarrhythmic action are found among the derivatives of 3-(3-isoxazolyl)chromones.

The interaction has been studied of a series of substituted 3-hetaryl-7-hydroxychromones with amino acids and formaldehyde (reactants ratio 1: 1: 2 respectively). In the case of glycine and Het = 3-isoxazolyl the product of aminomethylation at position 8 of the chromone was obtained, and with other Het (including Het = 4-phenyl-1,2,4-triazol-3-yl) 2-[6-alkyl-3-hetaryl-4-oxo-9,10-dihydro-4H,8H-chromeno[8,7-e][1,3]-oxazin-9-yl]acetic acids were formed. With β-alanine and Het = 4-phenyl-1,2,4-triazol-3-yl the corresponding β-substituted propionic acid was synthesized, but proline did not participate in the reaction, leading to bis(6-ethyl-3-hetaryl-7-hydroxychromon-8-yl)methane.

Isoflavones and their thiazole and pyrazole analogs are recyclized into the corresponding 4-(2-hydroxyphenyl)-pyrimidine derivatives under the effect of amidines. Their PMR spectra were studied. The effects related to the formation and strength of the intramolecular hydrogen bond were examined.

Isoflavone und ihre Heteroanaloga (I) reagieren mit Amidinen (II) in Gegenwart von Natriumethylat unter Recyclisierung zu Hydroxyphenylpyrimidinen (III).

3-(2-Benzimidazolyl)chromones with electron-donating and electron-withdrawing substituents and also chromones unsubstituted at position 2 were obtained by the reaction of alkyl-α-(2-benzimidazolyl)-2,4-dihydroxy-5-acetophenones with carboxylic acid anhydrides and chlorides. Reactions with cleavage and with retention of the pyrone ring were carried out.