Synthesis of π‐Functional Molecules through Oxidation of Aromatic Amines

Synthesis of two nitrogen-containing polyaromatic compounds through gold catalysis/DBU-promoted cyclizations

This work reports an efficient synthesis of novel benzo[7,8]indolizino[2,3,4,5-ija]quinazoline derivatives between 2-(2-ethynylaryl)acetonitriles 1 and anthranils 2. The synthetic approach involves the initial formation of 7-formylindole intermediates that can be implemented by DBU to activate a novel indole-nitrile-aldehyde cyclization.

Substitution and Orientation Effects on the Crystallinity and PFAS Adsorption of Olefin-Linked 2D COFs

Solid phase adsorbents with high removal affinity for per- and polyfluoroalkyl substances (PFAS) in aqueous environments are sought. We report the synthesis and investigation of COF-I, a new covalent organic framework (COF) with a good affinity for PFAS adsorption. COF-I was synthesized by the condensation reaction between 2,4,6-trimethyl-1,3,5-triazine and 2,3-dimethoxyterephthaldehyde and fully characterized. In addition to the high crystallinity and surface area, COF-I showed high hydrolytic and thermal stability. Further, we converted its hydrophobic surface to a hydrophilic surface by converting the ortho-methoxy groups to hydroxyl derivatives and produced a new hydrophilic olefin-linked two-dimensional (2D) COF. We experimentally measured the crystallinity of both COFs by X-ray diffraction and used atomistic simulations coupled with cross-polarization/magic angle spinning solid-state nuclear magnetic resonance (CP/MAS ssNMR) to determine the relative amounts of AA-stacking and AB-stacking present. COF-I, with its hydrophobic surface and methoxy groups in the ortho positions, showed the best PFAS adsorption. COF-I reduced the concentration of perfluorooctanoic acid from 20 to 0.069 μg L-1 and to 0.052 μg L-1 for perfluorooctanesulfonic acid. These amounts are lower than the U.S. Environmental Protection Agency advisory level (0.070 μg L-1). High efficiency, fast kinetic adsorption, and reusability of COF-I are advantages of COF-I for PFAS removal from water.

Synthesis of a novel tetra-phenol π-extended phenazine and its application as an organo-photocatalyst

In this paper, the synthesis of a novel tetra-phenol π-extended dihydrophenazine is reported. The obtained derivative presents marked reducing properties in the excited state and was exploited as an organo-photocatalyst in dehalogenation and C-C bond formation reactions. These results underline the great potential of functionalized π-extended dihydrophenazines as organo-photocatalysts.

A Strategy to Design Substituted Tetraamino-Phenazine Dyes and Access to an NIR-Absorbing Benzoquinonediimine-Fused Quinoxaline

The straightforward access to N- or C-substituted dinitro-tetraamino-phenazines (P1-P5) is enabled in oxidative conditions via formation of two intermolecular C-N bonds from accessible 5-nitrobenzene-1,2,4-triamine precursors. The photophysical studies revealed green absorbing and orange-red emitting dyes, with enhanced fluorescence in the solid state. Further reduction of the nitro functions led to the isolation of a benzoquinonediimine-fused quinoxaline (P6), which undergoes diprotonation to form a dicationic coupled trimethine dye absorbing beyond 800 nm.

Phenanthrene-Extended Phenazine Dication: An Electrochromic Conformational Switch Presenting Dual Reactivity

The synthesis and isolation of one of the few examples of a π-extended diamagnetic phenazine dication have been achieved by oxidizing a phenanthrene-based dihydrophenazine precursor. The resulting dication was isolated and fully characterized, highlighting an aromatic distorted structure, generated by the conformational change upon the oxidation of the dihydrophenazine precursor, which is also correlated with a marked electrochromic change in the UV–vis spectrum. The aromaticity of the dication has also been investigated theoretically, proving that the species is aromatic based on all major criteria (structural, magnetic, and energetic). Moreover, the material presents an intriguing dual reactivity, resulting in ring contraction to a π-extended triarylimidazolinium and reduction to the dihydrophenazine precursor, depending on the nature of the nucleophile involved. This result helps shed light on the yet largely unexplored reactivity and properties of extended dicationic polycyclic aromatic hydrocarbons (PAHs). In particular, the fact that the molecule can undergo a reversible change in conformation upon oxidation and reduction opens potential applications for this class of derivatives as molecular switches and actuators.

Unique Pseudo-Cross-Conjugated Mesomeric Betaines via an Iodate-Promoted Reaction of 3,3-Difluorocyclopropenes, Pyridines, and Anilines

A simple method for the synthesis of (E)-3-arylimino-3H-indolizin-4-ium-1-olates by an iodate-promoted multicomponent reaction between 3,3-difluorocyclopropenes, pyridines, and anilines was discovered. The reaction products belong to a limited and underexplored class of pseudo-cross-conjugated heterocyclic mesomeric betaines isoconjugated with odd nonalternant hydrocarbon anions, whose properties were studied. Reversible nucleophilic addition at the C5 position was revealed as their main chemical feature, which had an access to novel fully conjugated 1,5-dioxo-3-arylamino-1,5-dihydroindolizine and tetracyclic 4-oxo-4,6-dihydrocyclopenta[4,5]pyrimido[2,1,6-cd]indolizine ring systems in one step. Both the synthesis of betaines and their transformations demonstrate a high level of functional group compatibility, allowing the ready preparation of a number of structurally attractive compounds for materials or medicinal chemistry.

Electrochemical Organic Synthesis of Electron-Rich Biaryl Scaffolds: An Update

Biaryl scaffolds are widely spread in biologically important natural products, in numerous therapeutic agents, but they are also considered a privileged class of ligands and (organo)catalysts; therefore, the development of efficient alternative methodologies to prepare such compounds is always attracting much attention. The present review discusses the organic electrosynthesis of biaryls starting from phenols, anilines, naphthols, and naphthylamines. The most significant examples of the works reported in the last decade are presented and classified according to the single class of molecules: after the introduction, the first three sections relate to the reactions of phenols, naphthols, and anilines, respectively; the other two sections refer to cross-coupling and miscellaneous reactions.

Catalytic and Aerobic Oxidative Biaryl Coupling of Anilines Using a Recyclable Heterogeneous Catalyst for Synthesis of Benzidines and Bicarbazoles

In this study, a heterogeneous rhodium-catalyzed oxidative homocoupling reaction of anilines utilizing molecular oxygen as the sole oxidant is reported. Employing a commercially available and recyclable Rh/C catalyst enabled the oxidative dimerization of various anilines, including N,N-disubstituted and N-monosubstituted anilines, as well as diarylamines, triarylamines, and carbazoles. Additionally, the catalytic protocol was extended to the ortho-ortho coupling of anilines, affording 2,2'-diaminobiphenyls with high regioselectivity. Notably, the developed approach provides rapid access to diversely functionalized benzidines and diaminobiphenyls in an operationally simple, practical, and environmentally friendly manner.

Development of synthetic protocols for porphyrins and their analogs based on distorted structures — a SPP/JPP Young Investigator Award paper

Creation of novel [Formula: see text]-conjugated molecules is an important research topic. I describe in this account an approach to this aim that is based on the use of the distorted conformation of porphyrins. Planarization of distorted molecules enables the synthesis of heteroatom-containing porphyrin derivatives. Furthermore, dearomatization reaction proves effective to construct distorted conformations from planar [Formula: see text]-conjugated molecules under mild reaction conditions. According to this protocol, we have succeeded in the synthesis of heteroatom-containing curved-[Formula: see text] conjugated molecules that had never been achieved by conventional protocols. In particular, a nitrogen-embedded buckybowl is the first example of a buckybowl having a heteroatom in its central position, which exhibits unique properties due to the incorporation of the heteroatom in its curved [Formula: see text]-surface.

Copper-Catalyzed N,N-Diarylation of Amides for the Construction of 9,10-Dihydroacridine Structure and Applications in the Synthesis of Diverse Nitrogen-Embedded Polyacenes

We reported herein CuI/DMEDA catalyzed N,N-diarylation reaction of amides with various di(o-bromoaryl)methanes to produce diverse 9,10-dihydroacridine derivatives. The resulting 9,10-dihydroacridine derivatives were oxidized selectively under mild conditions to afford acridine, acridinone, and acridinium derivatives. The copper-catalyzed N,N-diarylation reaction coupled with oxidative aromatization reaction enabled the facile construction of nitrogen atom-embedded tetracenes and pentacenes of different ortho-fused patterns. The luminescence properties, especially the effect of fusion pattern on fluorescence emission of acquired N-polycenes, were also demonstrated.

Synthesis of Nitrogen-Containing Polyaromatics by Aza-Annulative π-Extension of Unfunctionalized Aromatics

Nitrogen-containing polycyclic aromatic compounds (N-PACs) are an important class of compounds in materials science. Reported here is a new aza-annulative π-extension (aza-APEX) reaction that allows rapid access to a range of N-PACs in 11-84 % yields from readily available unfunctionalized aromatics and imidoyl chlorides. In the presence of silver hexafluorophosphate, arenes and imidoyl chlorides couple in a regioselective fashion. The follow-up oxidative treatment with p-chloranil affords structurally diverse N-PACs, which are very difficult to synthesize. DFT calculations reveal that the aza-APEX reaction proceeds through the formal [4+2] cycloaddition of an arene and an in situ generated diarylnitrilium salt, with sequential aromatizations having relatively low activation energies. Transformation of N-PACs into nitrogen-doped nanographenes and their photophysical properties are also described.

Alchemy of donor–acceptor–donor multi-photofunctional organic materials: from construction of electron-deficient azaaromatics to exploration of functions

This Feature Article overviews the recent development of multi-photofunctional organic materials based on a twisted donor-acceptor-donor scaffold, which is driven by novel synthetic methods for exotic azaromatic compounds.