Palladium-Catalyzed Domino CH/NH Functionalization: An Efficient Approach to Nitrogen-Bridged Heteroacenes

Derivatization of 2,1,3-Benzothiadiazole via Regioselective C-H Functionalization and Aryne Reactivity

Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C-B bond, the first examples of ortho-directed C-H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.

Annulation reactions of electrophilic benzannulated heterocycles towards heteroacenes

The current review describes different annulation strategies reported with electrophilic benzannulated heterocycles for accessing heteroacenes. For the past two decades, the chemistry of electrophilic benzannulated heterocycles was extensively investigated, and several dipolar cycloadditions, metal and organo-catalyzed transformations were introduced for the generation of fused heterocycles. In this review, we have collected all the reports where the annulation of electrophilic benzannulated heterocycles results in a fully aromatic system, viz. heteroacenes with tri-, tetra-, and pentacyclic rings. We reviewed every paper on the synthesis of fused heterocycles that was accessible and categorized the review into several parts based on the electrophilic benzannulated heterocycle used in the heteroacene synthesis such as electrophilic indole, electrophilic benzothiophene, and so forth. The generality and mechanistic postulates of each methodology are highlighted. In addition, we have also tried to feature the advantages or shortcomings of each method and have mentioned the possible applications of these methodologies for accessing heteroacenes for material applications.

CuSO4-Catalyzed dual annulation to synthesize O, S or N-containing tetracyclic heteroacenes

In this work, CuSO4 is utilized as a practical redox catalyst for tandem dual annulation in the synthesis of indole-fused tetracyclic heteroacenes, which are important skeletons in both medicinal chemistry and materials chemistry. The preparation of such skeletons in a convenient and efficient manner is in high demand. This method realizes the modular synthesis of benzofuro-, benzothieno-, and indoloindoles from abundant feedstocks such as 2-halobenzyl halides and nitrile derivatives in up to 99% yields, providing a rapid access to diverse indole-fused heteroacenes with biological or optoelectronic properties.

Thienopyrrolo[3,2,1-jk]carbazoles: Building Blocks for Functional Organic Materials

The facile preparation of three regioisomeric thienopyrrolo[3,2,1-jk]carbazoles applying a convenient C-H activation approach is presented. The incorporation of thiophene into the triarylamine framework significantly impacted the molecular properties in comparison to the analogous indolo[3,2,1-jk]carbazole scaffold. Dependent on the exact substitution pattern, the absorption onsets of the new materials are shifted toward slightly higher wavelengths compared to the analogous indolo[3,2,1-jk]carbazole, whereas the emission maxima of the sulfur derivatives is shifted from 375 to 410 nm. In analogy, the HOMO-LUMO energy gap of the thienopyrrolo[3,2,1-jk]carbazoles is reduced compared to indolo[3,2,1-jk]carbazole. Therefore, the developed thienopyrrolo[3,2,1-jk]carbazoles enrich the family of triarylamine donors and constitute a novel building block for functional organic materials.

Synthesis of Thieno[3,2-b]indoles via Halogen Dance and Ligand-Controlled One-Pot Sequential Coupling Reaction

A two-pot synthesis of thieno[3,2-b]indole from 2,5-dibromothiophene is described. A halogen dance of 2,5-dibromothiophene was performed with LDA, and subsequent Negishi coupling was performed with 2-iodoaniline derivatives to provide the corresponding coupling products. The resulting two bromo groups have different reactivities, which were utilized for the one-pot Suzuki-Miyaura coupling/intramolecular Buchwald-Hartwig amination to produce thieno[3,2-b]indole via an assisted tandem catalysis that involved in situ ligand exchange.

Synthesis of indole-fused heteroacenes by cascade cyclisation involving rhodium(ii)-catalysed intramolecular C–H amination

Indole-fused heteroacenes have been synthesised from cascade cyclisation of 2-[(2-azidophenyl)ethynyl]anilines and -phenols in a catalytic manner under redox-neutral conditions.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Copper-catalyzed tandem arylation–cyclization of 2-alkynylaryl isothiocyanates with diaryliodonium salts: an efficient synthesis of thiochromeno[2,3-b]indoles

A Cu-catalyzed arylation–cyclization approach is developed for the synthesis of thiochromeno[2,3-b]indoles through the S-arylation, 5-endo-trig cyclization, and Friedel–Crafts-type cyclization sequence.

Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N(1)-Alkyne-1,2-diamines

A one-pot protocol for the diversity oriented synthesis of two N-polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N(1)-alkyne-1,2-diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6-endo-dig cyclization, 1,2-migration with ring expansion, and re-aromatization), or diazepine and triazole rings through 1,3-dipolar cycloaddition.