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Pyridinium ylides, along with related azaheterocyclic ylides, are widely used in synthetic organic chemistry. However, reactions that yield stable zwitterionic adducts from these ylides remain underexplored. In this work, we demonstrate that the reaction of pyrrole-2,3-diones with in situ-generated pyridine-based azomethine ylides affords stable zwitterionic adducts, which are typically transient species in analogous processes. These betaines are used as key intermediates for the synthesis of cyclopropane-fused pyrroles or pyridine-2,3-diones via thermolysis in chlorobenzene.

The reaction of 4,4-dimethyl-8-(4-methylbenzoyl)-3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazine-1,6,7-trione with thioacetamide in a 1:1 ratio when refluxed in dichloromethane gives (4S*,10aS*,11S*)-4-hydroxy-2,7,7-trimethyl-11-(4-methylbenzoyl)-7,8-dihydro-10H-4,10a-methano[1,4]oxazino[3,4-d][1,3,5]thiadiazepine-5,10(4H)-dione with a good yield. This compound was fully characterized.

1H-Pyrrole-2,3-diones, fused at [e]-side with a heterocycle, are suitable platforms for the synthesis of various angular polycyclic alkaloid-like spiroheterocycles. Recently discovered sulfur-containing [e]-fused 1H-pyrrole-2,3-diones (aroylpyrrolobenzothiazinetriones) tend to exhibit unusual reactivity. Based on these peculiar representatives of [e]-fused 1H-pyrrole-2,3-diones, we have developed an approach to an unprecedented 6/5/5/5-tetracyclic alkaloid-like spiroheterocyclic system of benzo[d]pyrrolo[3′,4′:2,3]pyrrolo[2,1-b]thiazole via their reaction with Schiff bases and carbodiimides. The experimental results have been supplemented with DFT computational studies. The synthesized alkaloid-like 6/5/5/5-tetracyclic compounds have been tested for their biotechnological potential as growth stimulants in the green algae Chlorella vulgaris.

A one-pot three-component synthesis of substituted meta -hetarylanilines from heterocycle-substituted 1,3-diketones has been developed. The electron-withdrawing power of the heterocyclic substituent (which can be estimated on the basis of calculated Hammett constants) in the 1,3-diketone plays a pivotal role in the studied reaction. The series of meta -hetarylanilines prepared (21–85% isolated yield) demonstrates the synthetic utility of the developed method.

Acyl(imidoyl)ketenes are highly reactive heterocumulenes that enable diversity-oriented synthesis of various drug-like heterocycles. Such ketenes, bearing heterocyclic substituents, afford angularly fused pyridin-2(1H)-ones in their [4+2]-cyclodimerization reactions. We have utilized this property for the development of a new synthetic approach to pharmaceutically interesting pyrido[2,1-b][1,3]benzothiazol-1-ones via the [4+2]-cyclodimerization of acyl(1,3-benzothiazol-2-yl)ketenes generated in situ. The thermal behaviors of 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones and 3-benzoylpyrrolo[2,1-b][1,3]benzothiazole-1,2-dione (two new types of [e]-fused 1H-pyrrole-2,3-diones reported by us recently) have been studied by thermal analysis and HPLC to elucidate their capability to be a source of acyl(1,3-benzothiazol-2-yl)ketenes. As a result, we have found that only 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones are suitable for this. The experimental results are supplemented with computational studies that demonstrate that thermolysis of 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones proceeds through an unprecedented cascade of two thermal decarbonylations. Based on these studies, we discovered a novel mode of thermal transformation of [e]-fused 1H-pyrrole-2,3-diones and developed a new pot, atom, and step economic synthetic approach to pyrido[2,1-b][1,3]benzothiazol-1-ones. The synthesized drug-like pyrido[2,1-b][1,3]benzothiazol-1-ones are of interest to pharmaceutics, since their close analogs show significant antiviral activity.

The 1,4-dipolar cycloaddition of the ylidene derivative of 1H-pyrrole-2,3-dione to a dipole generated in situ from 1-benzylbenzimidazole and dimethyl acetylenedicarboxylate proceeds via the exocyclic multiple bond of the ylidene derivative and affords a mixture of diastereomeric spiro[benzo[4,5]imidazo[1,2-a]pyridine-3,3’-pyrroles], which slowly epimerized in a solution.

4-Acyl-1H-pyrrole-2,3-diones fused at [e]-side with a heterocyclic moiety are suitable platforms for the development of a hetero-Diels–Alder-reaction-based, diversity-oriented approaches to series of skeletally diverse heterocycles. These platforms are known to react as oxa-dienes with dienophiles to form angular 6/6/5/6-tetracyclic alkaloid-like heterocycles and are also prone to decarbonylation at high temperatures resulting in generation of acyl(imidoyl)ketenes, bidentate aza- and oxa-dienes, which can react with dienophiles to form skeletally diverse products (angular tricyclic products or heterocyclic ensembles). Based on these features, we have developed an approach to two series of skeletally diverse 4H-1,3-oxazines (tetracyclic alkaloid-like 4H-1,3-oxazines and 5-heteryl-4H-1,3-oxazines) via a hetero-Diels–Alder reaction of 4-acyl-1H-pyrrole-2,3-diones fused at [e]-side with cyanamides. The products of these transformations are of interest for drug discovery, since compounds bearing 4H-1,3-oxazine moiety are extensively studied for inhibitory activities against anticancer targets.

Compounds based on the pyrazoloquinazoline scaffold are of significant interest in synthetic organic chemistry owing to their potential biological activity. In this work, we describe the synthesis of a new derivative with this scaffold, 9-oxo-2-(p-tolyl)-4,9-dihydropyrazolo[5,1-b]quinazoline-3a(3H)-carboxylic acid, obtained by reacting 2,4-dioxo-4-(p-tolyl)butanoic acid with 2-aminobenzohydrazide in a 1:1 ratio when mixed in ethanol. The compound was characterized by 1H/13C NMR, IR, and X-ray diffraction analysis.

The reaction of 5-(p-tolyl)furan-2,3-dione with thiourea in a 1:1 ratio when refluxed in 1,4-dioxane gives (Z)-N-carbamothioyl-4-hydroxy-2-oxo-4-(p-tolyl)but-3-enamide with a good yield. This compound was fully characterized.

The reaction of 3,3-diaminoacrylonitriles with DMAD and 1,2-dibenzoylacetylene was studied. It is shown that the direction of the reaction depends on the structure both of acetylene and of diaminoacrylonitrile. In the reaction of DMAD with acrylonitriles bearing a monosubstituted amidine group, 1-substituted 5-amino-2-oxo-pyrrole-3(2H)ylidenes are formed. On the other hand, a similar reaction of acrylonitriles containing the N,N-dialkylamidine group affords 1-NH-5-aminopyrroles. In both cases, pyrroles containing two exocyclic double bonds are formed in high yields. A radically different type of pyrroles containing one exocyclic C=C bond and sp3 hybrid carbon in the cycle is formed in reactions of 3,3-diaminoacrylonitriles with 1,2-diaroylacetylenes. As in reactions with DMAD, the interaction of 3,3-diaminoacrylonitriles with 1,2-dibenzoylacetylene can lead, depending on the structure of the amidine fragment, both to NH- and 1-substituted pyrroles. The formation of the obtained pyrrole derivatives is explained by the proposed mechanisms of the studied reactions.