LongLarf

Upon irradiation with visible light and sensitization with thioxanthen-9-one (TXT), substituted indoles undergo a facile and high-yielding hydrogen atom transfer/cyclization cascade to dearomatized, spirocyclic products.

Abstract

The photochemical synthesis of yet unknown 2-oxospiro[azetidine-3,3′-indolines] (17 examples, 80–95 % yield), 2,4-dioxospiro[azetidine-3,3′-indolines] (eight examples, 87–97 % yield), and 1-oxo-1,3-dihydrospiro[indene-2,3′-indolines] (17 examples, 85–97 % yield) is described. Starting from readily accessible 3-substituted indoles, a dearomatization of the indole core was accomplished upon irradiation at λ=420 nm in the presence of thioxanthen-9-one (10 mol%) as the sensitizer. Based on mechanistic evidence (triplet energy determination, deuteration experiments, by-product analysis) it is proposed that the reaction proceeds by energy transfer via a 1,4- or 1,5-diradical intermediate. The latter intermediates are formed by excited state hydrogen atom transfer from suitable alkyl groups within the C3 substituent to the indole C2 carbon atom. Subsequent ring closure proceeds with pronounced diastereoselectivity to generate a 4- or 5-membered spirocyclic dearomatized product with several options for further functionalization.

Various (benzo)thienoisoquinolines have been obtained by a straightforward three-step synthetic route based on site-selective Palladium catalysed cross-coupling reactions and a final Brønsted-acid mediated cycloisomerisation reaction as a key step. Steady-state optical and electrochemical properties of selected products have been determined, showing strong positive solvatochromism for donor-substituted derivatives.

Abstract

A variety of thieno[3,2-f]isoquinolines were prepared by combination of Pd catalysed cross-coupling reactions with Brønsted acid mediated cycloisomerisations. The reactions tolerate various functional groups and proceed with high selectivity. In addition, benzothieno[3,2-f]isoquinolines were prepared which represent a new heterocyclic core structure. The optical properties of selected compounds were studied by experimental and theoretical methods. Emission solvatochromism, characteristic of intramolecular charge transfer was observed for one of the compounds with a push-pull structure.

A novel synthetic method for metallabenzene was developed in which a phosphorus atom in a phosphinine ring is swapped with transition metal fragments. The oxidation of a phosphinine pincer iridium complex by O₂ afforded iridabenzene via exchange of the phosphorus atom and the iridium fragment. Dianionic rhodabenzene was synthesized by O₂ oxidation of an analogous rhodium complex, followed by reduction by metallic potassium.

Abstract

Herein, we report a novel method for the synthesis of metallabenzenes by swapping the phosphorus atom in an aromatic phosphinine ring with transition metal fragments. The oxidation of a phosphine-phosphinine-phosphine pincer iridium complex by O₂ triggered the replacement of the phosphorus atom of the phosphinine ring by an iridium fragment to afford iridabenzene. Dianionic rhodabenzene was also synthesized from a phosphinine rhodium complex by oxidation of the phosphorus atom, followed by subsequent reduction using metallic potassium. The aromaticity of the newly synthesized irida- and rhoda-benzenes was evaluated both experimentally and theoretically.

Nature Catalysis, Published online: 21 February 2022; doi:10.1038/s41929-022-00743-0

The Front Cover shows how the “Dehalogenato” spell allows to replace halogen atoms by hydrogens, using a heterogeneous nickel catalyst supported on titanium oxide in the presence of dihydrogen. The practicality of this catalyst system is demonstrated by the complete dehalogenation of environmentally hazardous and polyhalogenated substrates such as polybrominated diphenyl ethers and others. More information can be found in the Research Article by D. K. Leonard, P. Ryabchuk, et al.

Synthesis
DOI: 10.1055/s-0040-1719892

A straightforward Brønsted acid-catalyzed and scalable annulation of alkoxyallenes with simple naphthols was developed, affording chroman ketals in 49–84% yields. The versatile chroman ketals can be easily converted into coumarins by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidation, and a series of 2-substituted chromans via nucleophilic substitutions.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Synlett
DOI: 10.1055/a-1741-9069

Capitalizing on the propensity of 1,2-amino group migration in γ-aminocyclopentenone with a suitable promoter, gem-diaryl-equipped systems unfolded an unprecedented avenue for the Lewis acid promoted displacement of γ-aniline group with nucleophiles such as indole. Such transformation, besides providing a means for direct γ-functionalization of cyclopentenones, presented innumerable scope for β,γ-annulation. Various tailored indolo bisnucleophiles were explored in the current study that rendered an array of indole alkaloid-like compounds in excellent yields and selectivity through one-pot operation. Analysis of collective experimental observation along with designed control experiments strongly suggested the possibility of a retro aza-Piancatelli rearrangement, which is hitherto unknown in the context. Such repertoire could find potential applications in the synthesis of complex assemblies from the Piancatelli rearrangement and related processes.1 Introduction2 Aza-Piancatelli Rearrangement and Related Domino Processes3 An Unprecedented Aza-Piancatelli-Templated Strategy for Polycyclic Assemblies4 Summary and Outlook
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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