One Step Synthesis of 4,6,8-Trimethoxyazulenes - a General 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 %.

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).

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.

Iron Complexes of 4,5-Bis(diorganophosphinomethyl)acridine Ligands.

The search for an iron analog of the established ruthenium-based catalysts containing methylene-extended 4,5-bis(diorganophosphinomethyl)acridine ligands, [FeHCl(CO)(L)], resulted in the discovery of a bidentate coordination mode of these usually tridentate pincer ligands toward iron. The acridines nitrogen atom does not coordinate to iron, leading to the formation of iron diphos-type complexes with unusually large bite angles of up to 124° as well as bite angles around 155°. The iron-containing complexes [FeCl(κ-L)] (R = Pr, Ph), [FeX(κ-L)] (X = Cl, Br) and [Fe(CO)(κ-L)] (R = Pr, Cy) have been isolated in crystalline form and characterized by spectroscopic methods and mass spectrometry.

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.

Comparative study of the antiproliferative activity of heterometallic carbene gold(i)-platinum(ii) and gold(i)-palladium(ii) complexes in cancer cell lines.

The stepwise, one-pot synthesis of heterobimetallic carbene gold(i) platinum(ii) complexes from readily available starting materials is presented. The protecting group free methodology is based on the graduated nucleophilicities of aliphatic and aromatic amines as linkers between both metal centers. This enables the selective, sequential installation of the metal fragments.

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.

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.

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.

Easy Access to Functionalized Indolines and Tetrahydroquinolines via a Photochemical Cascade Cyclization Reaction.

Herein, the development of a light-mediated synthesis of functionalized indolines and tetrahydroquinolines is reported. These structural motifs are considered as highly valuable targets, attributed to their widespread occurrence in pharmaceuticals and natural products. The gold-mediated approach offers a direct route to functionalized indolines in yields of up to 81% under mild photochemical conditions.

Helically Chiral π-Expanded Azocines Through Regioselective Beckmann Rearrangement and Their Charged States.

We report a synthetic approach to π-expanded [6]helicenes incorporating tropone and azocine units in combination with a 5-membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8-membered lactam, azocine, and amine units. As shown by X-ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state.

Metal- and solvent-free domino reaction of 2-isocyanophenol esters to benzoxazines: long-range 1,5-acyl migration on 1,4-diazabutatriene.

The first example of intramolecular nucleophilic addition of 1,4-diazabutatriene to ester is disclosed. This approach provides a facile and versatile synthesis for functionalized 2-1,4-benzoxazines under metal-, reagent-, and solvent-free conditions. Experimental and computational studies revealed the pivotal role of 1,5-acyl migration as the self-catalytic step in the reaction selectivity.

Indenoannulated Tridecacyclene: An All-Carbon Seven-Stage Redox-Amphoter.

We disclose an indenoannulated tridecacyclene comprising a central cyclooctatetraene moiety with multiple adjacent pentagonal rings which is accessible in a concise synthetic sequence. The saddle-shaped geometry of the non-benzenoid polycyclic scaffold and its unique packing behavior in the solid state were characterized by X-ray crystallography. In electrochemical studies, the compound undergoes seven reversible redox events comprising five reductions and two oxidations.

Gold(I)-Catalyzed Intramolecular 7-endo-dig Cyclization of Triene-Yne Systems: New Access towards Azulenothiophenes.

We report the direct synthesis of new azulene derivatives through gold-catalyzed cyclization reactions. A five-membered ring as backbone in the applied triene-yne substrates turned out to be crucial to induce the 7-endo-dig cyclization mode necessary to trigger azulene formation. The obtained targets are of high interest due to their potential applications in different fields, like organic materials, medicine or cosmetics.

Synthesis and structural properties of -diselenopyrazines.

Recently, dithienopyrazines have emerged as promising building blocks in the field of materials science, showcasing their potential as hole-transport materials in organic electronic devices. Herein, we report the synthesis of its heavier analogues, the diselenopyrazines, along with an analysis of their optoelectronic and structural properties. In the acquired crystal structures, interesting molecular packing motifs suitable for potential device fabrication were observed.

Stabilizing Azaheptacenes.

The symmetrical 7,16-diaza-6,8,15,17-tetrakis(triisopropylsilylethynyl)heptacene was obtained by a Pd-catalyzed reaction of a 2,3-diamino-1,4-diethynylanthracene with a 2,3-dibromo-1,4-diethynyl anthracene. Positioning the TIPS-ethynyl groups adjacent to the central ring suppresses dimerization via [4+4] cycloadditions and Diels-Alder reactions; the middle pyrazine ring renders this species stable to oxidation. A single crystal structure was obtained, and thin film transistors with μ = 0.

Transition-metal-free intramolecular double hydrofunctionalization of alkyne to access 6/7/5-fused heterocyclic skeletons.

We describe a novel intramolecular double hydrofunctionalization cyclization of alkyne with nitrogen and oxygen nucleophilic groups to construct valuable 6/7/5-fused heterocyclic products. This post-Groebke-Blackburn-Bienaymé (GBB) reaction introduces a new class of functionalized isocyanides. Transition-metal-free cyclization, broad substrate scope, and high atom economy were some features of the present protocol.