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The article presents Fe(II)/Et3N-Relay-Catalyzed Domino Reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives.

A diazo approach toward functionalized naphtho[1,2- d ]imidazole derivatives has been developed. It involved a new reaction of arylamidines with 2-(α-diazoacyl)-2 H -azirines giving 5-aryl-4-(α-diazoacyl)-1 H -imidazoles under mild conditions in good yields. The mechanism of annulation of azirines with amidines is discussed based on DFT calculations. The reaction proceeds in an unusual manner by cleavage of the azirine C-C bond, allowing for the transfer of the aryl substituent from the arylamidine to the proper position of the key intermediate of naphtho[1,2- d ]imidazole synthesis. Under thermolysis conditions, 5-aryl-4-(α-diazoacyl)-1 H -imidazoles undergo Wolff rearrangement followed by the selective 6π-cyclization of transient ketene to form 3 H -naphtho[1,2- d ]imidazoles bearing various substituents in the positions 2,3,4,5,7,8,9. Additionally, variation of the substituents at position 5 of naphtho[1,2- d ]imidazoles is possible through the formation of triflates and subsequent cross-coupling reactions. One more heterocyclic pharmacophoric skeleton, 3 H -furo[3',2':3,4]naphtho[1,2- d ]imidazole, was easily constructed from methyl 5-hydroxy-3 H -naphtho[1,2- d ]imidazole-4-carboxylates in a one-pot mode using O-alkylation with phenacyl bromides followed by base-induced intramolecular acyl substitution at room temperature with high yields.

A divergent diazo approach toward alkyl 5/4-hydroxy-3 H -benzo[ e ]indole-4/5-carboxylates has been developed. The reaction of 1,3-diketones with alkyl 2-diazo-3-oxo-3-(2 H -azirin-2-yl)propanoates catalyzed by Co(acac) 3 or Ni(acac) 2 gives various alkyl 3-(1 H -pyrrol-2-yl)-2-diazo-3-oxopropanoate in good yields. The latter undergo Wolff rearrangement followed by the 6π-cyclization of transient ketene to form alkyl 5-hydroxy-3 H -benzo[ e ]indole-4-carboxylates bearing various substituents in positions 1, 2, 7, and 8, as well as derivatives of methyl 4-hydroxy-6 H -thieno[2,3- e ]indole-5-carboxylates and methyl 5-hydroxy-7 H -benzo[ c ]carbazole-6-carboxylate under thermolysis or Rh 2 (OAc) 4 catalysis. Isomeric benzoindoles, alkyl 4-hydroxy-3 H -benzo[ e ]indole-5-carboxylates, have been prepared by Boc-protection of the pyrrole nitrogen of alkyl 3-(1 H -pyrrol-2-yl)-2-diazo-3-oxopropanoates followed by an intramolecular formal carbene insertion into the aromatic C-H bond catalyzed by Cu(OTf) 2 . The hydroxyl group of alkyl 5/4-hydroxy-3 H -benzo[ e ]indole-4/5-carboxylates, through the formation of the corresponding triflates, allows the introduction of various substituents into the 5/4 position of benzo[ e ]indoles using the cross-coupling reaction and even form a new heterocyclic backbone, benzo[ k ]pyrrolo[2,3- i ]phenanthridine, via a tandem Suzuki reaction/nucleophilic acyl substitution.

A diazo strategy for the intramolecular azirine ring expansion was developed. Azirinyl-substituted diazodicarbonyl compounds, prepared from diazoacetylazirines, were converted in excellent yields to 2-hydroxy-3-oxo-2,3-dihydro-1 H -pyrrole-2-carboxylates under Rh catalysis in the presence of water. According to DFT calculations, the formation of only pyrrolinone derivatives and the absence of O-H insertion products of Rh carbene into water are due to the low Gibbs free energy of the transition state for the concerted opening of the azirine ring and recyclization to pyrrolone in intermediate Rh complexes.

Invited for the cover of this issue are the groups of Sergey P. Tunik and his colleagues from St Petersburg University. The image depicts the strong bathochromic shift of the emission wavelength of phosphorescent platinum(II) complexes upon their aggregation in the presence of water. Read the full text of the article at 10.1002/chem.202202207., (© 2022 Wiley-VCH GmbH.)

α-Diazopyrroles selectively react with enamines at room temperature to give either (4+2)-cycloaddition-dehydroamination cascade products, pyrrolo[2,1- c ][1,2,4]triazines, or azo coupling products. The reaction was used for the synthesis of functionalized ortho -fused heterocycles with new tetrahydrobenzo[ e ]pyrrolo[2,1- c ][1,2,4]triazine and tetrahydro-6 H -cyclohepta[ e ]pyrrolo[2,1- c ][1,2,4]triazine frameworks. Unstable azo compounds, 2-[(2-aminovinyl)diazenyl]pyrroles, were obtained from enamines of tetralone or acyclic ketones. According to the density functional theory calculations, (4+2)-cycloaddition of α-diazopyrroles with enamines proceeds in a nonconcerted manner via the zwitterionic intermediate, which undergoes cyclization to pyrrolotriazine or a competitive 1,5-prototropic shift leading to the formation of azo coupling product.

The synthesis of 5-aryl- and 4-aryl/hetaryl/cyclopropyl/alkynyl-5-aryl-1 H -pyrrole-2,3-diones by formal isomerization of isoxazole-5-carbaldehydes mediated Mo(CO) 6 in wet MeCN has been developed. The resulting 1 H -pyrrole-2,3-diones are good precursors for substituted 1 H -pyrrolo[2,3- b ]quinoxalines.

The Co(III)-catalyzed reaction of 1,3-dicarbonyl compounds with 2-(diazoacetyl)-2 H -azirines, prepared by a simplified procedure from 2 H -azirin-2-carbonyl chlorides, led in high yields to the formation of 2-(diazoacetyl)pyrroles, while leaving the diazoacetyl function intact. The intramolecular aromatic substitution reaction of 2-(diazoacetyl)pyrroles, catalyzed by Cu(OTf) 2 , provided selectively previously unknown benzo[ e ]- and hetero[ e ]-fused indol-7-oles in good yields. Formylation of benzo[ e ]indol-4-ol led selectively to the 5-formyl derivative, which is a good precursor for an unusual salen ligand and its Ni-complex. Triflates prepared from benzo[ e ]indol-4-oles gave various 4-substituted benzo[ e ]indoles carrying aryl, 2-thienyl, 2-pyridyl, and alkynyl groups, in excellent yields using cross-coupling reactions. 4-(2-Pyridyl)benzo[ e ]indoles, upon treatment with BF 3 ·Et 2 O/Et 3 N, afforded a new type of fluorescent boron complexes with large Stokes shifts.

2-(1 H-Pyrazol-1-ylcarbonyl)-2 H-azirines were synthesized by in situ trapping of 2 H-azirine-2-carbonyl chlorides, generated by Fe(II)-catalyzed isomerization of 5-chloroisoxazoles, with pyrazoles. According to DFT calculations, the selectivity of nucleophilic substitution at the carbonyl group of 2 H-azirine-2-carbonyl chloride by a pyrazole nucleophile, which is a mixture of two tautomers, is controlled by thermodynamic factors. 2-(1 H-Pyrazol-1-ylcarbonyl)-2 H-azirines are excellent precursors for the preparation of two other pyrazole-nitrogen heterocycle dyads: 5-(1 H-pyrazol-1-yl)oxazoles by photolysis and 1-(1 H-pyrrol-2-ylcarbonyl)-1 H-pyrazoles by a Ni(II)-catalyzed reaction with 1,3-dicarbonyl compounds. 5-(1 H-Pyrazol-1-yl)oxazoles show strong emission in acetonitrile at 360-410 nm with high quantum yields.