Synthesis of Annulated Anthracenes, Carb­azoles, and Thiophenes Involving Bradsher-Type Cyclodehydration or Cycli­zation-Reductive-Dehydration Reactions

Chiral Iodotriptycenes: Synthesis and Catalytic Applications

New iodotriptycenes, including some chiral derivatives, have been synthesised, and their catalytic potential towards oxidative transformations has been investigated. The enantioselectivities observed in the products using chiral iodotriptycene catalysts are low, probably owing to the large distances between the coordinating groups and the iodine moieties in these compounds.

Regiodivergent CDC reactions of aromatic aldehydes with unactivated arenes controlled by transient directing strategy

The regiodivergent catalytic dehydrogenative cross-coupling reactions at both sp² and sp³ hybridized carbons of aromatic compounds are particularly challenging. Herein, we report the finding of transient directing group controlled regiodivergent C(sp³)-C(sp²) and C(sp²)-C(sp²) cross-coupling in the o-methyl benzaldehyde frameworks. Catalyzed by palladium, using K₂S₂O₈ or [F⁺] reagents as by-standing oxidants and unactivated arenes as substrates/solvents, various benzyl benzaldehydes or phenyl benzaldehydes were prepared. A mechanism study indicated that the regiospecificity is dominated by the [5,6]-fused palladacycle or [6,5]-fused palladacycle intermediates, which are generated from Pd-chelation with specified transient directing groups and further C-H activations.

Recent advances in the syntheses of anthracene derivatives

Anthracene and anthracene derivatives have been extensively studied over the years because of their interesting photophysical, photochemical, and biological properties. They are currently the subject of research in several areas, which investigate their use in the biological field and their application in OLEDs, OFETs, polymeric materials, solar cells, and many other organic materials. Their synthesis remains challenging, but some important preparative methods have been reported, especially in the last decade. This review presents an update of the recent strategies that have been employed to prepare anthracene derivatives. It encompasses papers published over the last twelve years (2008–2020) and focuses on direct and indirect methods to construct anthracene and anthraquinone frameworks.

An attempt to synthesize a terthienyl-based analog of indacenedithiophene (IDT): unexpected synthesis of a naphtho[2,3-b]thiophene derivative

We report herein our attempt to synthesize an analog of indacenedithiophene (IDT) based on a tetraphenylhexyl substituted, covalently bridged syn-terthienyl unit. Instead of the expected compound the adopted synthetic route led to the formation of an unexpected, new naphtho[2,3-b]thiophene derivative. The structure of this compound was fully characterized by NMR and HRMS as well as single crystal X-ray diffraction and its electronic properties have been analyzed by UV-vis absorption spectroscopy and cyclic voltammetry. A possible mechanism for the formation of this compound is also proposed on the basis of detailed theoretical investigations.

Serendipitous synthesis of a novel naphtho[2,3-b]thiophene derivative. Detailed investigation of the structure and properties as well as a possible mechanism for its formation.

Synthesis, structure and properties of semi-internally BN-substituted annulated thiophenes

A series of semi-internally BN-substituted annulated thiophenes were synthesized from easily accessible 2,1-borazaronaphthalenes.

Lewis acid-mediated synthesis of mono- and tris-indole adducts from chiral aziridines

Lewis acid-mediated regio- and stereoselective nucleophilic addition of 2- or 3-substituted indoles to non-activated aziridine-2-carboxaldehydes in dioxane afforded 2-(indol-3-ylhydroxymethyl)aziridines whose ring opening with various nucleophiles rendered multi-substituted tryptamine derivatives. The reaction of the same aziridine-2-carboxaldehyde with three moles of indole in dichloromethane yielded tris-indole adducts β-(3,3'-bisindolyl)methyl (BIM) tryptamines from sequential steps including nucleophilic addition to aldehyde, Michael type Friedel-Crafts alkylation of the mono-adduct followed by regio- and stereoselective ring-opening of the aziridine ring.

A Modular Approach to Phosphorescent π-Extended Heteroacenes

A modular route to previously inaccessible classes of ring-fused π-extended heteroacenes bearing the heavy inorganic element tellurium (Te) is presented. These new materials can be viewed as n-doped analogs of molecular graphene subunits that exhibit color tunable visible light phosphorescence in the solid state and in the presence of air. The general mechanism of phosphorescence in these systems was probed experimentally and computationally via time-dependent density functional theory (TD-DFT). The incorporation of Te into π-extended oligoacene frameworks was achieved by an efficient Zr/Te transmetalation protocol; related zirconium-element exchange reactions have been used to prepare both electron-rich and electron-deficient heterocycles containing different elements from throughout the p-block. Therefore, the current study provides a clear path to incorporate inorganic elements into heteroacenes of greater complexity and side group selectivity compared to existing synthetic routes.

Syntheses of 7-Substituted Anthra[2,3- b]thiophene Derivatives and Naphtho[2,3- b:6,7- b']dithiophene

7-R-Anthra[2,3- b]thiophene derivatives (1, R = H, Me, i-Pr, or MeO) are prepared in three steps (in average overall yield >50%) starting from ( E)-4-RC₆H₄CH₂(HOCH₂)C═CI(CH₂OH). The latter are commercial or readily prepared from 2-butyne-1,4-diol and ArCH₂Cl (both costing <1 cent/mmol) at 10 g scales. These allow for the selective formation of (otherwise unattainable) higher solubility 7-derivatives. Similar methods allow for the preparation of naphtho[2,3- b:6,7- b']dithiophene 2 using equally low-cost starting materials.

Reductive Aromatization/Dearomatization and Elimination Reactions to Access Conjugated Polycyclic Hydrocarbons, Heteroacenes, and Cumulenes

Acenes, heteroacenes, conjugated polycyclic hydrocarbons, and polycyclic aromatic hydrocarbons (collectively referred to in this review as conjugated polycyclic molecules, CPMs) have fascinated chemists since they were first isolated and synthesized in the mid 19th century. Most recently, these compounds have shown significant promise as the active components in organic devices (e.g., solar cells, thin-film transistors, light-emitting diodes, etc.), and, since 2001, a plethora of publications detail synthetic strategies to produce CPMs. In this review, we discuss reductive aromatization, reductive dearomatization, and elimination/extrusion reactions used to form CPMs. After a brief discussion on early methods to synthesize CPMs, we detail the use of reagents used for the reductive (de)aromatization of precursors containing 1,4-diols/diethers, including SnCl₂ and iodide (I^- ). Extension of these methods to carbomers and cumulenes is briefly discussed. We then describe low-valent metal species used to reduce endoxides to CPMs, and discuss the methods to directly reduce acenediones and acenones to the respective acene. In the final section, we describe methods used to affect aromatization to the desired CPM via extrusion of small, volatile molecules.

Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes

A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar¹ CH₂ (HOCH₂ )C=C(CH₂ OH)I (Ar¹ =Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH₂ )C=C(CH₂ OH)I, accessed from ultra-low cost HOCH₂ C≡CCH₂ OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar¹ CH₂ (HOCH₂ )C=C(CH₂ OH)CH₂ Ar² (Ar² =Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar¹ CH₂ (CHO)C=C(CHO)CH₂ Ar² , which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.

Synthetic transformation of 1,3-diarylisobenzofuran-DMAD adducts: a facile preparation of tri-substituted α-naphthols

1,3-Diarylisobenzofuran-DMAD adducts upon reaction with BF₃·OEt₂ in DCM at room temperature underwent a regiospecific 1,2-aryl migration followed by the Krapcho decarboxylation to give tri-substituted α-naphthols in good yields.