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The reaction of 6-amino-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles with phosphorus sulfide in boiling pyridine leads to the formation of the unexpected [1,2]oxaphosphinino[6,5-c]pyrazoles. The structure of the products was confirmed with 2D Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray analysis.

A new highly efficient method for the condensation of (indol-3-yl)carbaldehydes with 2-methylazoles and 2-methylazines under activation with microwave irradiation is developed. The method provides high yields of structural scaffolds of bishetarylethylene fluorescent sensors that found widespread application in medicinal, bioorganic, and pharmaceutical chemistry.

3-Substituted 2-quinolones are obtained via a novel metal-free transannulation reaction of 2-nitroolefins with 2-substituted indoles in polyphosphoric acid. This acid-mediated cascade transformation operates via the ANRORC (Addition of Nucleophile, Ring Opening, and Ring Closure) mechanism and can be used in combination with the Fisher indole synthesis to offer a practical three-component hetero-annulation approach to 2-quinolones from arylhydrazines, 2-nitroalkenes, and acetophenone. An alternative entry to this chemistry employing the alkylation of electron-rich arenes and hetarenes with 1-(2-indolyl)-2-nitroalkene has also been demonstrated.

Triethylammonium salts of (4-aryl-3-cyano-6-oxo-1,4,5,6-tetrahydropyridin-2-yl)malononitriles were prepared by reaction of aldehydes with Meldrum's acid and 2-amino-1,1,3-tricyanopropene (malononitrile dimer) in the presence of triethylamine. Upon treatment with alpha-mercaptocarbonyl compounds in the presence of alkali, new thieno[2,3-h][1,6]naphthyridines were prepared in good yields.

The reaction of 4-hydroxy-7,7-dimethyl-7,8-dihydro-6H-chromen-2,5-dione with aldehydes and malononitrile afforded new pyrano[3,2-c]chromenes. Upon treatment of 4-hydroxy-7,7-dimethyl-7,8-dihydro-6H-chromen-2,5-dione with anilines and triethyl orthoformate, new 3-anilinomethylidene 7,8-dihydro-2H-chromen-2,4,5(3H,6H)-triones were synthesized.

A new approach to 1,3-diazapyrenes via peri annelation of perimidines with 1,3-dicarbonyl compounds is developed. It is demonstrated that this method has a number of advantages compared to a previously reported procedure employing chalcones as electrophilic components. The new method can be used for efficient double peri annelation of biperimidines with 1,3-dicarbonyl compounds affording 2,2′-bi-1,3-diazapyrenes.

A method has been developed for the nitration of 6(7)-acylperimidines using sodium nitrite in formic acid. The reaction gives a mixture of 4(9)-, 9(4)-, and 7(6)-nitro-6(7)-acylperimidines from which the latter can be separated by extraction with chloroform. Reduction of the 6(7)-acyl-7(6)-nitro- perimidines yields 1H-1,5,7-triazacyclopenta[cd]phenalenes. Subsequent Schmidt reaction and reduction give 1,3,6,8-tetraazapyrenes.

The reactions of phloroglucinol with α,β-unsaturated dinitriles (or malononitrile and carbonyl compounds) lead to the formation of hitherto unknown 2,8-diamino-5-hydroxy-4H,10H-pyrano[2,3-f]chromene-3,9-dicarbonitriles. The reaction conditions and the structure of the products were studied in details.

Methods have been developed for the synthesis of 1,3-diazapyrenes, 8(6)-aryl-6(8)-oxo-1,6,7,8-tetra-hydro-1,3-diazapyrenes, and 1,3,7-triazapyrenes based on a three-component reaction of perimidines with 1,3,5-triazines and carbonyl compounds, benzonitrile, or vinyl butyl ether in polyphosphoric acid.

A new method of carboxyamidation of aromatic compounds based on their reaction with nitromethane in polyphosphoric acid has been developed. Upon the hydrolysis of benzamides during the reaction mixture workup, the corresponding benzoic acids can be obtained.

A new method for the synthesis of 4H-benzo[de]isoquinolin-4-ones has been developed, based on the reaction of 2-naphthyl ethers with an equimolar quantity of 1,3,5-triazines in polyphosphoric acid. With a 2.5 molar excess of 1,3,5-triazines in polyphosphoric acid, the products of 1,6-diacylation (diformylation) are formed. Isoquino[6',5',4':10,5,6]anthra[2,1,9-def]isoquinoline is formed upon reaction of a 1.5 molar excess of 1,3,5-triazine with naphthalene in polyphosphoric acid at 130-140 °C.

Published data on the recyclization reactions of 1,3,5-triazines are reviewed. The classification is based on the fragments of the 1,3,5-triazine molecules used in the construction of new heterocycles.

Methods have been developed for the synthesis of 1,3-diazapyrenes based on the reactions of perimidines with ethoxymethylene-1,3-dicarbonyl compounds and also 6(7)-benzoyl(acetyl, formyl)perimidines with carbonyl compounds in PPA.

A novel three-component synthesis has been developed for 1,3-diazapyrenes based on the reaction of 1,8-naphthalenediamine with triazine and carbonyl compounds in polyphosphoric acid (PPA). The use of benzonitrile in place of the carbonyl compounds in this reaction gives 6-phenyl-1,3,7-triazapyrenes.

A method has been developed for the synthesis of 1,3,7-triazapyrenes using the reaction of 6(7)-formyl-and 6(7)-benzoylperimidines with 1,3,5-triazines in PPA. Under these conditions, 6(7)-formylperimidine reacts with 2,4,6-trimethyl-1,3,5-triazine to give 6-hydroxy-1,3-diazapyrene.

A new effective synthetic method for 1,3-diazapyrenes and 1,3,7-triazapyrenes is developed based on the three-component reaction of perimidines or 1,8-diaminonaphthalene with 1,3,5-triazines and carbonyl compounds or benzonitrile in polyphosphoric acid (PPA).

The reaction of phenylenediamines and 2-aminophenols (I) with nitroalkanes (II) in PPA leads to desired benzimidazoles and benzoxazoles (III) in high yields, whilst the reaction with 2-nitro-1-phenylethan-1-one (IV) affords unexpected 2-phenyl substituted products.

The title compounds are obtained by a novel acid-mediated cascade transformation via the ANRORC (addition of nucleophile, ring opening, and ring closure) mechanism.

A modular approach to 3-substituted 2-quinolones via a cascade annulation reaction between 4-nitroketones and hydrazines has been developed.

PPA-induced umpolung triggers efficient nucleophilic addition of unactivated anilines to nitroalkanes to produce N-hydroxyimidamides. The latter undergo sequential acid-promoted cyclocondensation with ortho-OH or ortho-NHR moieties to afford benzoxazoles and benzimidazoles, respectively.

Polynuclear aromatic and heteroaromatic compounds with peri-annelated fiveand six-membered rings include perimidine derivatives and show a range of useful properties. The development of novel, efficient methods for preparation of such compounds is a current challenge. Although methods for preparing perimidines containing a pyrrole ring are quite numerous [1-3], there are only very limited ways for synthesizing aceperimidines [3-5]. Such methods can be based on the dinitration of acenaphthene, reduction of the nitro derivative, and subsequent cyclization using various reagents. The drawback of such methods is the large number of stages. In our work, we propose a method of synthesizing aceperimidines from the available 4-acetyland 4-benzoylacenaphthenes 1a-e, using a system of reagents developed at our laboratories [6-8]. It was found that reaction of ketones 1a-e with a fourfold excess of sodium azide in polyphosphoric acid (PPA) for 1 h at 70-80°C, followed by 4 h at 100-110°C gave the aceperimidines 3a-e in 27-46% yields.

Previously unknown tetraazapyrene derivatives of type (III) are prepared in a one-pot procedure.

Possible reaction mechanisms leading to both peri-anellation products (III) and (IV) are proposed.

A modular approach to 3-substituted 2-quinolones via a cascade annulation reaction between 4-nitroketones and hydrazines has been developed.

The importance of indole derivatives as biologically active compounds is difficult to overestimate. Benzo[c,d]indoles are not an exception; for example, efficient inhibitors of thymidylate synthase were found among compounds of this series [1]. The present communication describes the synthesis of fused benzo[c,d]indole derivatives, 6H-pyrrolo[2,3,4-gh]perimidines IVa–IVc, from naphthalene-1,4,8-triamine (I) and 1,3,5-triazines IIa–IIc. We previously showed that 1,3,5-triazine in polyphosphoric acid (PPA) acts as efficient formylating and acylating agent [2–5], in particular toward naphthylamines [5]. Therefore, it may be expected that the use of 1,3,5-triazine should ensure convenient synthesis of pyrroloperimidines IVa–IVc. In fact, by heating triamine I with triazines IIa–IIc in PPA first at 80–90°C and then at 130–140°C we obtained the corresponding pyrroloperimidines IVa–IVc in 38–48% yield. The reaction is likely to involve intermediate formation of aminoperimidines IIIa–IIIc. Unlike the known procedure [6], the proposed method requires no preliminary preparation and acylation of perimidines. Furthermore, the key step in the known procedure [6] is the Schmidt reaction utilizing sodium azide in acid medium, and there exists a risk of evolution of toxic and explosive hydrazoic acid. The procedure proposed by us is free from the said disadvantage.

Nitration of acylperimidines (I) using NaNO2 in formic acid gives predominantly the 6(7)-nitro-derivatives (II), which can be smoothly transformed into tetraazapyrenes (IV) via a Schmidt Reaction, or triazacyclopentaphenalenes (V) via simple Zn-reduction.

3-Substituted 2-quinolones are obtained via a novel, metal-free transannulation reaction of 2-substituted indoles with 2-nitroalkenes in polyphosphoric acid. The reaction can be used in conjunction with the Fisher indole synthesis offering a practical three-component heteroannulation methodology to produce 2-quinolones from arylhydrazines, 2-nitroalkenes and acetophenone.

Polynuclear aromatic and heteroaromatic compounds with peri-annelated fiveand six-membered rings include perimidine derivatives and show a range of useful properties. The development of novel, efficient methods for preparation of such compounds is a current challenge. Although methods for preparing perimidines containing a pyrrole ring are quite numerous [1-3], there are only very limited ways for synthesizing aceperimidines [3-5]. Such methods can be based on the dinitration of acenaphthene, reduction of the nitro derivative, and subsequent cyclization using various reagents. The drawback of such methods is the large number of stages. In our work, we propose a method of synthesizing aceperimidines from the available 4-acetyland 4-benzoylacenaphthenes 1a-e, using a system of reagents developed at our laboratories [6-8]. It was found that reaction of ketones 1a-e with a fourfold excess of sodium azide in polyphosphoric acid (PPA) for 1 h at 70-80°C, followed by 4 h at 100-110°C gave the aceperimidines 3a-e in 27-46% yields.

2,3'-Biquinolyl dianion reacts with organolithium and organomagnesium compounds with the formation, after treatment of the reaction mixture with water, of 2'-alkyl(aryl)-1',2'-dihydro-2,3'-biquinolyls, and, after treatment of the reaction mixture with alkyl halides, of 1'-alkyl-2'-alkyl(aryl)-1',2'-dihydro-2,3'-biquinolyls. The reaction includes attack of the nucleophilic reagent with an electron transfer to a molecule of solvent.

A new method of acetamidation of aromatic compounds based on their reaction with nitroethane in polyphosphoric acid has been developed. Upon the hydrolysis of acetamides during the reaction mixture workup, the corresponding amines can be obtained.

A method for the synthesis of 1,3-diazapyrenes has been developed based on the reaction of 1H-perimidines with 1,3-dicarbonyl compounds in polyphosphoric or 70% aq. sulfuric acid.

Methods have been developed for the synthesis of 1,3-diazapyrenes based on the reactions of 1-methylbenzo[f]quinazolines with DMF dimethyl acetal or with 1,3,5-triazine in PPA.

An effective synthesis of various azapyrenes from phenalenes and their dihydro derivatives has been developed using 1,3,5-triazines in polyphosphoric acid (PPA).

With alkyl chlorides and alkyl phenyl ethers the dianion of 2,3′-biquinolyl forms the products from alkylation at position 4′. Their treatment with alkyl halides or water gives 1′, 4′-dialkyl-1′, 4′-dihydro-2,3′-biquinolyls or 4′-alkyl-1′,4′-dihydro-2,3′-biquinolyls respectively.

The 2,3′-biquinolyl dianion, when reacting with aryl- and hetaryl halides, forms arylation products at the 4′ position, and treatment of these products with alkyl halides or water yields 1′-alkyl-4′-aryl-1′,4′-dihydro-2,3′-biquinolyls or 4′-aryl-1′,4′-dihydro-2,3′-biquinolyls, respectively. Oxidation of the latter yields 4′-aryl-2,3′-biquinolyls. The cation dependence of the arylation reaction is demonstrated.

Previously unknown tetraazapyrene derivatives of type (III) are prepared in a one-pot procedure.

1,3-Diazapyrenes (IV) and (VI), tetrahydro-1,3-diazapyrenes (VIII) and 1,3,7-triazapyrenes (IX) are synthesized by three-component reactions of perimidines (I).

A new method for the relatively easy introduction of carbamoyl and carboxyl groups into activated aromatic compounds is presented.

The tandem transformation Schmidt-reaction—nitrosation—heterocyclization leads to previously unknown tetraazacyclopenta[c,d]phenalenes (II) together with N-oxides (III) as main products.

A method for the synthesis of 8-hydroxy-1,3,6-triazapyrenes (II) is given and a possible reaction mechanism is proposed.