Palladium‐Catalyzed Annulation of 1,2‐Diborylalkenes and ‐Arenes with 1‐Bromo‐2‐[( Z )‐2‐bromoethenyl]arenes: A Modular Approach to Multisubstituted Naphthalenes and Fused Phenanthrenes

Producing aryl halides from lignin

Lignin represents the most abundant biomass resource, which contains aromatic units. Lignin refinery is a promising, sustainable alternative for the production of aromatic chemicals. However, depolymerization and transformation of lignin into aryl halides, which are indispensable chemicals in both the academic and industrial communities, remain challenging. Here, we report a simple and mild method for the depolymerization and halogenation of lignin, leading to the production of useful aryl halides. Notably, hydrogen bond activation for halogenation reagents is essential for substantially increasing the reactivity, resulting a highly efficient cleavage of C-C bonds in lignin. This method is highly selective for breaking C(sp2)-C(sp3) bonds of lignin linkages, enabling the application of precise depolymerization and halogenation reactions from lignin models to native lignin from various wood resources, which provides a sustainable and efficient access to various synthetically useful aryl halides.

Dearomatizing Photocyclization and Oxidative Aromatization: Constructing Polycyclic Arenes from Styrenes

The direct construction of polycyclic arenes through ring formation using simple building blocks is highly appealing but remains challenging in organic chemistry. In this study, we introduce an efficient cascade reaction that combines dearomatizing photocyclization with oxidative aromatization, driven by organophotocatalysis. Conducted under mild, transition-metal-free conditions, this reaction seamlessly converts styrene derivatives into a diverse array of functionalized polycyclic aromatic compounds with good yields and regioselectivity. This approach provides a straightforward and economical route to valuable polycyclic arenes, starting from readily available and abundant styrene derivatives.

Zipping up tetraazaperylene: synthesis of tetraazacoronenes via double coupling in the bay positions

Substituted tetraazacoronene fluorophores have been obtained selectively by double Suzuki-Miyaura cross coupling of symmetrically substituted 1,2-bis(pinacolatoboryl)alkenes with a bay-substituted octaazaperopyrenedioxide (OAPPDO). Subsequent Scholl reaction of the dimethoxyphenylated derivative allowed further π-extension of the azaperylene core, yielding a highly redox-active bis(phenanthro)tetraazacoronene.

Tetraazacoronenes and Their Dimers, Trimers and Tetramers

Tetraazacoronenes were synthesized from bay-functionalized tetraazaperylenes by Zr-mediated cyclization and four-fold Suzuki-Miyaura cross coupling. In the Zr-mediated approach, an η4 -cyclobutadiene-zirconium(IV) complex was isolated as an intermediate to cyclobutene-annulated derivatives. Using bis(pinacolatoboryl)vinyltrimethylsilane as a C2 building block gave the tetraazacoronene target compound along with the condensed azacoronene dimer as well as higher oligomers. The series of extended azacoronenes show highly resolved UV/Vis absorption bands with increased extinction coefficients for the extended aromatic cores and fluorescence quantum yields of up to 80 % at 659 nm.

Aza-Henry Reaction: Synthesis of Nitronaphthylamines from 2-(Alkynyl)benzonitriles

A transition-metal-free approach for construction of nitronaphthylamines has been developed for the first time through aza-henry, chemoselective, and regioselective annulation of 2-alkynylbenzonitriles with nitromethane. In addition, the strategy provides an elegant, operationally simple and atom-economical route for the synthesis of nitroamino substituted heterocyclic scaffolds, featuring a range of sensitive functional groups. The reaction could also devise acetonitrile and acetophenone as nucleophile. The protocol has been successfully implemented for late-stage modification of bioactive molecules.

A palladium-catalyzed multi-component annulation approach towards the synthesis of phenanthrenes

An efficient palladium-catalyzed three-component cascade reaction has been developed for the facile construction of phenanthrene frameworks. The transformation is driven by a controlled reaction sequence of Suzuki-Miyaura coupling followed by the insertion of alkynes, and finally, annulation to yield phenanthrene derivatives via C-H activation. This methodology is able to accommodate a variety of substrates and affords the anticipated products in good to excellent yields.

Hydrogen-Bond-Controlled Formal Meta-Selective C-H Transformations and Regioselective Synthesis of Multisubstituted Aromatic Compounds

The meta-selective introduction of functional groups into aromatic substrates was successfully achieved by hydrogen-bond-controlled meta-selective C-H borylation and successive conversion of the boryl group to other functional groups. By this method a wide range of functional groups could be introduced without isolation of the borylated intermediates. The desired meta-functionalized aromatic products were obtained in a one-pot manner even on a gram scale. Regioselective synthesis of multisubstituted aromatic compounds was also achieved.

5,10-Dimesityldiindeno[1,2-a:2',1'-i]phenanthrene: a stable biradicaloid derived from Chichibabin's hydrocarbon

A diindenophenanthrene biradicaloid, formally derived from Chichibabin's hydrocarbon, is obtained in a short, scalable synthesis.

A diindenophenanthrene biradicaloid, formally derived from Chichibabin's hydrocarbon, is obtained in a short, scalable synthesis. The present system is electron-rich and devoid of conjugated substituents, and still exhibits very good stability under ambient conditions. The introduction of the diindeno[1,2-a:2′,1′-i] phenanthrene ring framework results in a singlet biradicaloid system with an easily accessible triplet state (ΔE_S–T = –1.30 kcal mol^–1) and a small electronic bandgap (1.39 V). The stability limits of the title hydrocarbon were explored systematically in the solid state, to reveal an unusual thermally initiated hydrogen-scrambling oligomerization process.

Metal-free naphthannulation reactions of yne-allenone esters for accessing polycyclic aromatic hydrocarbons

The first metal-free base-promoted naphthannulation reactions of yne-allenone esters were developed for the direct assembly of a wide range of polycyclic aromatic hydrocarbons with generally good yields.

Catalytic Double Carbon-Boron Bond Formation for the Synthesis of Cyclic Diarylborinic Acids as Versatile Building Blocks for π-Extended Heteroarenes

The first catalytic synthesis of cyclic diarylborinic acids is developed using a dihydroaminoborane reagent as the boron source. Unlike previously reported methods that use organolithium reagents, this method allows the easy synthesis of cyclic diarylborinic acids bearing a range of functionalities including CN, CO₂ Et, CONEt₂ and NMeCO₂^t Bu. Furthermore, these cyclic diarylborinic acids provide rapid access to skeletal diversity, in particular they enable the synthesis of six- to nine-membered π-extended heteroarenes through simple cross-coupling reactions, which are important synthetic targets in both advanced materials and pharmaceuticals.

Accessing molecularly complex azaborines: palladium-catalyzed Suzuki-Miyaura cross-couplings of brominated 2,1-borazaronaphthalenes and potassium organotrifluoroborates

Despite their potential applications in both medicinal chemistry and materials science, there have been limited reports on the functionalization of 2,1-borazaronaphthalenes since their discovery in 1959. To access new chemical space and build molecular complexity, the Suzuki–Miyaura cross-coupling of brominated 2,1-borazaronaphthalenes has been investigated. The palladium-catalyzed cross-coupling proceeds with an array of potassium (hetero)aryltrifluoroborates in high yield with low catalyst loadings under mild reaction conditions. By the use of a high-yielding bromination of various 2,1-borazaronaphthalenes to generate electrophilic azaborine species, a library of 3-(hetero)aryl and 3,6-diaryl-2,1-borazaronaphthalenes has been synthesized.

Metal-catalyzed annulation reactions for π-conjugated polycycles

The progress of the metal-catalyzed annulation reactions toward construction of various π-conjugated polycyclic cores with high conjugation extension is described. This article gives a brief overview of various annulation reactions promoted by metal catalysts including C-H bond functionalization, [2+2+2] cycloaddition, cascade processes, ring closing metathesis, electrophilic aromatization, and various cross-coupling reactions. A variety of conjugated polycycles with planar, bowl-shaped, and helical structures have been constructed in high efficiency and selectivity.

Synthesis of naphthalene amino esters and arylnaphthalene lactone lignans through tandem reactions of 2-alkynylbenzonitriles

A novel and efficient synthesis of naphthalene amino esters and arylnaphthalene lactone lignans via the tandem reaction of 2-alkynylbenzonitriles is presented.

Regio- and stereocontrolled access to γ-boronated unsaturated amino esters and derivatives from (Z)-alkenyl 1,2-bis(boronates)

The Borono-Mannich reaction of (Z)-1-alkene-1,2-diboronic esters proceeded regioselectively at the terminal C-B bond to afford (E)-γ-boronated unsaturated amino esters in good yields. These compounds were then subjected to Suzuki couplings for the creation of diversely substituted olefinic amino acid systems. Several other functional transformations were also carried out to illustrate the synthetic utility of the Petasis products.