Transition-Metal-Free Radical Approach for the Synthesis of Isothiocyanates by Pyridinium 1,4-Zwitterionic Thiolates as a Sulfur Source.

Herein, we disclose a novel, mild, transition-metal-free approach to synthesizing diversely functionalized isothiocyanates from the corresponding isocyanide precursors, achieving high to excellent yields (up to 97%). The current method sheds light on the reactivity of pyridinium 1,4-zwitterionic thiolates as an unprecedented sulfur source strikingly distinct from their previously known reactivity in ionic annulation reactions, showcasing an innovative approach to organic synthesis.

Nickel-Catalyzed Three-Component Carboamination/Cyclization of Alkynes To Access 2,3-Disubstituted Quinolines.

Presented herein is a nickel-catalyzed chemo- and regioselective three-component tandem carboamination and cyclization of terminal alkynes with organoboronic acids and anthranils for facile and modular access to 2,3-substituted quinolines. In this process, anthranil has dual roles: serving as an electrophilic aminating reagent and a redox buffer to suppress the generation of an off-cycle Ni(0) complex. Moreover, the anionic acetylacetonate (acac) ligand was found to be vital to ensure a productive Ni(I)-Ni(III)-Ni(I) catalytic cycle.

Stepwise reduction of an asymmetric π-expanded pyracylene towards the crystalline radical trianion.

The chemical reduction of a pyracylene-hexa--hexabenzocoronene-(HBC)-fused nanographene TPP was investigated with K and Rb metals to reveal its multi-electron acceptor abilities. The reaction of TPP with the above alkali metals, monitored by UV-vis-NIR and H NMR spectroscopy, evidenced the stepwise reduction process. The use of different solvents and secondary ligands enabled isolation of single crystals of three different reduced states of TPP with 1, 2, and 3 electrons added to its π-system.

One Step Synthesis of 4,6,8-Trimethoxyazulenes - as Building Block for 2-Functionalized Azulenes.

Here we present a simple gold-catalyzed one-pot reaction of easily available diarylbutadiynes, with trimethoxybenzene as solvent and reactant to synthesize 4,6,8-trimethoxyazulenes. The methoxy substituents, which render the azulene very electron-rich, enable a change of azulenes typical regioselectivity for electrophilic substitutions, which enables facile electrophilic 2-substitution with iodine, bromine, chlorine, selenium or sulfur. Especially the 2-haloazulenes which can usually only be obtained through lengthy multistep syntheses are valuable building blocks for the synthesis of 2-substituted azulene derivatives.

A Trithia-Bridged N-Heterotriangulene: The Hitherto Missing Electron Donor.

The very first representative of trithia-bridged N-heterotriangulene, a triphenylamine with sulfur atoms bridging the ortho-positions, was synthesized by a sequence of regioselective sulfenylation with phthalimidesulfenyl chloride followed by Lewis acid-catalyzed electrophilic cyclization. X-ray crystallography revealed a saddle-shaped geometry of the polycyclic scaffold. UV/Vis absorption spectroscopy and cyclic voltammetry were used to characterize the optoelectronic properties.

Gold-Catalysed Intramolecular Reaction of Alkynes with Sulfoximines Acting as N- and O-Transfer Reagents.

Among the nucleophilic oxidants employed in the gold-catalysed oxidation of alkynes, sulphur-based reagents have played a substantial role since the beginning, granting access to the respective gold carbene intermediates. Herein, we describe the first example of the substance class of sulfoximines being used as atom transfer reagents to alkynes in gold catalysis. Based on the transformation of N-(2-alkynylphenyl) sulfoximines to 3H-indol-3-ones, it is demonstrated that the sulfoximine functionality is capable of selectively transferring first its nitrogen moiety to the alkyne, forming the α-imino gold carbene, which is then oxidised by the released sulfoxide moiety in a second step via a pseudo-intramolecular mechanism-a distinctive feature that differentiates this work mechanistically from earlier studies.

Gold-Catalyzed Access to Pyrrolo- and (Aryl)Indolo-Fused Phenazines.

Novel fused phenazines were synthesized through a combination of gold-catalyzed hydroamination and cascade cyclization reactions towards azaacenes. In total, 30 new compounds were synthesized and investigated with respect to their structural and optoelectronic properties. In solution, these targets exhibit strong green to red emission, with quantum yields of up to 60 %.

Moiré Lattice of Twisted Bilayer Graphene as Template for Non-Covalent Functionalization.

We present a novel approach to achieve spatial variations in the degree of non-covalent functionalization of twisted bilayer graphene (tBLG). The tBLG with twist angles varying between ~5° and 7° was non-covalently functionalized with 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN) molecules. Our results show a correlation between the degree of functionalization and the twist angle of tBLG.

Diastereoselective Construction of Spirocyclic Isobenzofurans via a Tandem Michael Addition/5-Exo-dig Cyclization Reaction.

A practical approach for rapid and efficient access to spirocyclic isobenzofurans is described. The reaction proceeds through the cycloaddition of 1,6-ynenone derivatives and 4-nitro-1,3-diarylbutan-1-ones, promoted by CsCO in the presence of -proline as a catalyst. The advantages of this reaction include the formation of two C-C bonds and one C-O bond as well as mild reaction conditions.

Revisiting Butafulvene Formation by Thermal Dimerization of Fluorene-Based Dialkynes - Effects of Aromatic Substituents.

Butafulvenes, together with pentafulvenes and [3]radialenes, form a series of constitutional benzene isomers in which aromaticity changes significantly and can be strongly substituent dependent. Butafulvene, as a member of this series, is frequently proposed to be antiaromatic. Based on butafulvenes Hopf, Zimmerman and coworkers first time described, derivatives thereof were synthesized and the effects of substituents on both the stability of the intermediate isobenzenes and on their optoelectronic and (anti)aromatic properties are discussed.

Diels-Alder Reactivity of Triisopropylsilyl Ethynyl Substituted Acenes.

We investigated the Diels-Alder reaction of 6,13-bis(triisopropylsilylethynyl)pentacene (1) with small dienophiles such as (bridged) dihydronaphthalenes/cyclohexenes that yielded adducts at the central ring, the other dienophiles predominantly or exclusively attacked the unsubstituted off-center ring. The difference in regioselectivity was investigated by DFT calculations. Apart from dispersion interactions, it is due to the steric demand of the dienophiles, which need to fit in between the silylethynyl substituents to react at the central ring.

High-Yielding Nanobelt Formation by Chirality-Assisted Synthesis.

Shape-persistent conjugated nanobelts (CNBs) are fascinating synthetic targets. However, in most cases these are made in low overall yields by applying strategies of macrocyclization followed by (multiple) ring fusion reactions for nanobelt formation. Here, we describe the high yielding synthesis of enantiopure chiral nanobelts in 84 % yield by applying chirality-assisted synthesis (CAS).

CCC-NHC Au(iii) pincer complexes as a reliable platform for isolating elusive species.

The reactivity of unprecedented CCC-NHC Au(iii) pincer complexes has been investigated, employing a novel methodology for their preparation. Notably, this marks the inaugural case of CCC-NHC Au(iii) pincer complexes with a central aryl moiety where the two arms of the pincer ligand consist of N-heterocyclic carbenes (NHC). The stability conferred by the CCC-NHC ligand facilitated the isolation of elusive Au(iii) species, encompassing Au(iii)-formate, Au(iii)-F, Au(iii)-Me, and Au(iii)-alkynyl.

Breaking Strong Alkynyl-Phenyl Bonds: Poly(-phenylene ethynylene)s under Mechanical Stress.

Stronger chemical bonds withstand higher mechanical forces; thus, the rupture of single bonds is preferred over the rupture of double or triple bonds or aromatic rings. We investigated bond scission in poly(dialkyl--phenylene ethynylene)s (PPEs), a fully conjugated polymer. In a scale-bridging approach using electron-paramagnetic resonance spectroscopy and gel permeation chromatography of cryomilled samples, in combination with density functional theory calculations and coarse-grained simulations, we conclude that mechanical force cleaves the sp-sp bond of PPEs (bond dissociation energy as high as 600 kJ mol).

A Negatively Curved Nanographene with Four Embedded Heptagons.

Negatively curved nanographenes are considered as cutouts of three-dimensional fully sp-hybridized carbon allotropes such as Schwarzites. Here we present the synthesis of a C cut-out of the Schwarzite 8-4-1-p proposed by Lenosky et al. and investigate its optical as well as electrochemical properties.

Substituent Effects in Scholl-Type Reactions of 1,2-Terphenyls to Triphenylenes.

A series of 3,3''- and 4,4''-dimethoxy terphenyls with different second substituents on their ortho-positions have been synthesized and investigated upon the possibility to be oxidatively cyclodehydrogenated to the corresponding triphenylenes under Scholl-type conditions. The experimentally obtained selectivities were supported and explained by quantum chemical calculations and conclusions on the involved mechanisms (acid catalyzed arenium-ion mechanism (AIM) vs radical cation mechanism) were drawn.

Tosylhydrazide-Induced 1,6-Enyne Radical Cyclization under Copper Catalysis: Access to 3,4-Dihydronaphthalen-1(2)-one Derivatives.

We describe an approach to access 4-aroyl-3-aryl-3,4-dihydronaphthalen-1(2)-one derivatives in 41-79% yields through the Cu-catalyzed radical cyclization/desulfonylation of 1,6-enynes with tosylhydrazide under air conditions. This alternative desulfonylation strategy combines mild conditions, external oxidant-free processes, and sustainability, contributing to more environmentally friendly organic synthesis. The mechanistic studies showed that the CuCl/O combination serves as the source of the oxygen atom needed to form the C═O bond.

Electrochemical meta-C-H sulfonylation of pyridines with nucleophilic sulfinates.

Considering the indispensable significance and utilities of meta-substituted pyridines in medicinal, chemical as well as materials science, a direct meta-selective C-H functionalization of pyridines is of paramount importance, but such reactions remain limited and highly challenging. In general, established methods for meta C-H functionalization of pyridines rely on the utilization of tailored electrophilic reagents to realize the intrinsic polarity match. Herein, we report a complementary electrochemical methodology; diverse nucleophilic sulfinates allow meta-sulfonylation of pyridines through a redox-neutral dearomatization-rearomatization strategy by a tandem dearomative cycloaddition/hydrogen-evolution electrooxidative C-H sulfonation of the resulting oxazino-pyridines/acid-promoted rearomatization sequence.

Azaacene Diradicals Based on Non-Kekulé Meta-Quinodimethane with Large Two-Photon Cross-Sections in the Infrared Spectral Region.

Non-Kekulé quinoidal azaacences m-A (1 a,b) were synthesized and compared to their para- and ortho-quinodimethane analogues. m-A display high diradical characters (1 b: y = 0.88) due to their meta-quinodimethane (m-QDM) topology.

Copper(II)-Catalyzed Amination of Aryl Chlorides in Aqueous Ammonia.

Anilines are ubiquitous in bio-active compounds and their synthesis can be achieved via metal-catalyzed cross-coupling reactions involving aryl halides. We describe an unusual, yet simple, Cu-catalyzed system for the amination of aryl chlorides in pure aqueous ammonia with 2.5 mol % catalyst loading under non-inert conditions.

Gold Meets Selenium: Dual Activation of Selenium-Containing Propargyl Alcohols Towards the Synthesis of 2H-Chromenes and Mechanistic Insights.

Herein, we report the synthesis of seleno-substituted chromenes from selenoalkynes and phenols. In this cascade reaction, the applied gold catalyst not only functions as a π-acid, but also as a Lewis acid, enabling the propargylic substitution in the first step to connect the oxygen carbon bond. Under the optimal reaction condition a total of 26 chromenes were accessible by this modular access.

Selective Coupling of β-(Borylvinyl)silanes by a Gold-Catalyzed Hiyama Reaction-An Easy Way to Diaryl-Substituted Vinyl Boronates.

The use of diaryl-substituted vinyl boronates, a class of chemical building blocks with well-known synthetic utility, is principally limited by the difficulty faced in their preparation. Herein, we present a convenient synthetic strategy based on a gold-catalyzed Hiyama arylation of (Z)-β-(borylvinyl)silanes, which are easily accessible by hydroboration of silylalkynes. By exploiting the highly electronegative nature of the gold(III) intermediate (which is accessed by light-assisted oxidation using aryl diazonium salts), a selective activation of the silyl group in the presence of the boron moiety is achieved.

Tandem mass spectrometry of π-expanded triphenylamine and N-heterotriangulene scaffolds: Radical cation versus silver(I) adduct.

Triphenylamine (TPA) and N-heterotriangulene (N-HTA) scaffolds with up to three oligophenyl extensions are investigated by electrospray ionization (tandem) mass spectrometry (ESI-[MS/]MS). Due to their low oxidation potentials, all molecules readily form radical cations in the electrospray process. The energy-resolved collision-induced dissociation behaviour of the molecular ions is contrasted to that of the silver(I) adducts.

Synthesis of 2,3-Dihydrobenzofurans via a Photochemical Gold-Mediated Atom Transfer Radical Addition Reaction.

A light-mediated cyclization reaction initiated by an atom transfer radical addition (ATRA) of haloalkanes onto alkenes was exploited for the synthesis of functionalized dihydrobenzofurans. Initial investigation indicated that the dimeric gold catalyst [Au(μ-dppm)Cl] can effectively be used for intermolecular ATRA reactions. Further, the reactivity was applied in a cascade-like cyclization for the preparation of dihydrobenzofuran derivatives.