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A potential of using nickel complexes with 1,3-dicarbonyl compounds for the transformation of heterocyclic aminonitriles into fused systems with a 4-aminopyridine core was evaluated. A possibility of introducing acidophobic groups into the molecules of fused compounds was shown.

A versatile and efficient three-component cyclization of methyl 4-(o-hydroxyphenyl)-2,4-dioxobutanoates 1, N-substituted isatins 2, and primary amines 3 was explored to synthesize of 2H-spiro[chromeno[2,3-c]pyrrole-1,3'-indoline]-2',3,9-triones. We obtained a library of 122 derivatives with an indolin-2-one motif as an important structural fragment in natural alkaloids. This method is practical and useful strategy for constructing dihydrochromeno[2,3-c]pyrrole-3,9-diones. Most of the obtained products also have functional groups for easy and further diversification by classical reactions.

Graphic abstract An efficient and practical synthetic procedure for libraries of diversified 1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones using a multicomponent process is presented. A convenient synthetic procedure for obtaining functionalized 3-(2-hydroxyphenyl)-4,5-dihydropyrrolo[3,4-c]pyrazol-6(1H)-ones via ring-opening strategy has also been developed. This protocol was found to be compatible with a wide range of substituents and paves the way for the practical synthesis of title compounds with a broad range of substituents under mild condition. The products can be easily isolated by crystallization without the use of chromatography. Supplementary Information The online version contains supplementary material available at 10.1007/s11030-021-10234-2.

A preparative method for the synthesis of 1-alkyl-3-methyl-1,4-dihydropyrazolo[4,3-c]pyrazoles was developed. The alkylation of the obtained compounds with halocarboxylic acid esters was also investigated. A principal possibility of creating libraries of compounds based on pyrazolo[4,3-c]pyrazole derivatives was shown.

Alkylation of 4-(phenylthio)-1H-pyrazol-5-ols with methyl bromoacetate has afforded a series of phenyl pyrazolyl sulfides which have been oxidized into sulfones. The resulting esters have been hydrolyzed into the corresponding acids. The synthesized compounds potentially exhibit biological activity.

Methyl o-hydroxybenzoylpyruvate heated with N,N-dimethylethylenediamine and aromatic aldehydes affords in a high yield 5-aryl-3-hydroxy-4-(2-hydroxyphenyl)-1-[2-(dimethylamino)ethyl]-1,5-dihydro-2H-pyrrol-2-ones, which easily split off water at boiling in acetic acid and are converted into 1-aryl-2-[(2-dimethylamino)ethyl]-1,2-dihydrochromeno[2,3-c]pyrrol-3,9-diones. The developed route of synthesis provides a wide range of derivatives of 1-aryl-2-[ω-(dialkylamino)alkyl]-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones.

A preparative procedure for the synthesis of 2-alkyl-1-aryl-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones from methyl 4-(o-hydroxyphenyl)-2,4-dioxobutanoate, aromatic aldehyde, and aliphatic amine is described.

Available N-(1,2,2,2-tetrachloroethyl)dichloroacetamide selectively reacts with trialkyl phosphites and triphenylphosphine, which was used for preparing polycentered electrophilic agents unusually reacting with piperidine and morpholine in the presence of water to give in high yields 4-dialkoxyphosphoryl- or 4-triphenylphosphonio-substituted oxazole-2-carbaldehydes containing piperidine or morpholine moiety in the 5-position. Their structure was determined by spectroscopy and also by chemical transformations into phenylhydrazones, thiosemicarbazones, aminals, and other functional derivatives of these two types of phosphorus-containing aldehydes of the oxazole series.

The spectral and quantum-chemical study of phosphonium ylides derivatives of 2‑oxazoline-5-one with both conjugated and non-conjugated substituents were performed. It was shown that considerable positive charge is located at phosphorus atom, whereas the substantial negative charge is fixed at sulfur atom. It has been found from the calculations and 13 C NMR spectral data that introducing of the non-conjugated and conjugated substituents in the position 2 of the oxazole cycle in thiaphosphonium ylides causes only small change in the molecular equilibrium geometry and in charge distribution in oxazole moiety, whereas spectral characteristics of substituted derivatives are very sensitive to the nature of the lowest electron transitions which reflects in changes of their absorption maxima.

Previously it was found that methyl o-hydroxybenzoylpyruvate was easily converted into 1,2-diaryl[1], 1-aryl-2-heteryl[2], or 2-alkyl-1-aryl-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones [3]. Isatin and its N-alkyl derivatives are known to behave in many transformations like aromatic aldehydes. We found that the short-time heating of equimolar amounts of methyl ohydroxybenzoylpyruvate I, N-methylisatin II, and aliphatic amines IIIa, IIIb in methanol afford spiro derivatives of 3-hydroxy-3-pyrrolin-2-one IVa, IVb in high yield. This three-component cyclocondensation has been well studied [4], but isatin and its derivatives have not been used as carbonyl components. Pyrrole derivatives IV possess acidic properties and form adducts with aliphatic amines. Compound IVb exists as an internal salt. Similar adducts with monoethanolamine were described [5].

The substituted vinylphosphonium salts of the general formula RCClC (NCClAr)P+Ph3 Cl− react with an excess of sodium azide in a peculiar manner. As a result, phosphonium ylides are produced. They are stabilized with a nitrile and a 5-aryltetrazol-1-yl group or with two substituted tetrazolyl residues as confirmed by X-ray structural analysis. All the ylides obtained exhibit low reactivity and do not enter into the Wittig reaction, but one of them was found to undergo the following sequence of transformations: NC C P(⧸)(⧹) → H2NCO C P(⧸)(⧹) → (⧹) (⧸)PNCOCH2.

Treatment of 1-phosphorylated 2,2-dichloroethenylcarboxamides with excess hydrazine hydrate gives in high yields phosphorylated derivatives of 2-alkyl(aryl)-5-hydrazinooxazoles containing the P(O)(OCH3)2, P(O)(OC2H5)2, and P+(C6H5)3ClO4- groups in the 4-position of the ring. The presence of the hydrazine group in these oxazole derivatives was confirmed not only by the spectral data, but also by the reactions with p-toluic aldehyde, p-toluic chloride, and phenyl isothiocyanate.

Pyrano[2,3-c]pyrroles constitute a poorly explored class of fused heterocyclic compounds. We have found only one publication where the synthesis of such compounds containing an alkoxycarbonyl or carboxy group in the 2-position has been described [1]. We have developed a new synthetic approach to pyrano [2,3-c]pyrrole-4,7-dione derivatives on the basis of methyl (E)-6-phenyl-2,4-dioxohex-5-enoate (I) [2]. By heating equimolar amounts of compound I, aromatic aldehyde IIa or IIb, and 2-aminothiazole (III) in glacial acetic acid for a short time we obtained the corresponding 5-aryl-3-hydroxy-4-(3-phenylprop-2enoyl)-1-(1,3-thiazol-2-yl)-1,5-dihydro-2H-pyrrol-2ones IVa and IVb in moderate yield. Compounds of type IV have been reported previously [3]. The structure of pyrroles IVa and IVb was confirmed by elemental analyses and IR and H NMR spectra. On heating in DMSO in the presence of a catalytic amount of iodine, compounds IVa and IVb underwent intramolecular cyclization to 5-aryl-2-phenyl-6-(1,3thiazol-2-yl)-5,6-dihydropyrano[2,3-c]pyrrole-4,7-diones Va and Vb, respectively. Such cyclization with formation of pyran ring is used in the chemistry of chromone [4, 5]. DOI: 10.1134/S1070363208080331