Chiral Teropyrenes: Synthesis, Structure, and Spectroscopic Studies.

We present the inaugural synthesis of a chiral teropyrene achieved through a four-fold alkyne benzannulation catalyzed by InCl3, resulting in good yields. The product underwent thorough characterization using FT-Raman and FT-IR spectroscopies, demonstrating a close agreement with calculated spectra. X-ray crystallographic analysis unveiled a notable twist in the molecule's backbone, with an end-to-end twist angle of 51°, consistent with computational predictions. Experimentally determined enantiomeric inversion barriers revealed a significant energy barrier of 23 kcal/mol, facilitating the isolation of enantiomers for analysis by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopies. These findings mark significant strides in the synthesis and characterization of chiral teropyrenes, offering insights into their structural and spectroscopic properties.

Hexabenzoheptacene: A Longitudinally Multihelicene Nanocarbon with Local Aromaticity and Enhanced Stability.

We report the synthesis of a longitudinally helical molecular nanocarbon, hexabenzoheptacene (HBH), along with its dimethylated derivative (HBH-Me), which are composed of six benzene rings periodically benzannulated to both zigzag edges of a heptacene core. This benzannulation pattern endows the resulting nanocarbons with a helical heptacene core and local aromaticity, imparting enhanced solubility and stability to the system. The chiral HBH-Me adopts a more highly twisted conformation with an end-to-end twist angle of 95°, enabling the separation of the enantiomers. Both HBH and HBH-Me can be facilely oxidized into their corresponding dications, which exhibit enhanced planarity and aromaticity upon loss of electrons. Notably, both longitudinally helical nanocarbons readily promote solid state packing into two-dimensional (2D) arrangement. Single-crystal microbelts of HBH-Me show hole mobility up to 0.62 cm2 V-1 s-1, illustrating the promising potential of these longitudinally helical molecules for organic electronic devices.

Heterocycle-guided synthesis of m-hetarylanilines via three-component benzannulation.

A one-pot three-component synthesis of substituted meta-hetarylanilines from heterocycle-substituted 1,3-diketones has been developed. The electron-withdrawing power of the heterocyclic substituent (which can be estimated on the basis of calculated Hammett constants) in the 1,3-diketone plays a pivotal role in the studied reaction. The series of meta-hetarylanilines prepared (21-85% isolated yield) demonstrates the synthetic utility of the developed method.

[2+2+1+1] Cycloaddition for de novo Synthesis of Densely Functionalized Phenols.

A unique benzannulation strategy for regioselective de novo synthesis of densely functionalized phenols is described. Through metal-mediated formal [2+2+1+1] cycloaddition of two different alkynes and two molecules of CO, a series of densely functionalized phenols were obtained. The benzannulation strategy allows efficient regioselective installation up to five different substituents on a phenol ring. The resulting phenols have a substitution pattern different from those obtained from Dötz and Danheiser benzannulations.

Facile Synthesis and Chiral Resolution of Expanded Helicenes with up to 35 cata-Fused Benzene Rings.

Expanded helicenes are expected to show enhanced chiroptical properties as compared to the classical helicenes but the synthesis is very challenging. Herein, we report the facile synthesis of a series of expanded helicenes Hn (n=1-4) containing 11, 19, 27 and 35 cata-fused benzene rings through Suzuki coupling-based oligomerization followed by Bi(OTf)3 -mediated regioselective cyclization of vinyl ethers. Their structures were determined by X-ray crystallographic analysis. Enantiopure H2, H3, and H4 can be isolated by chiral HPLC and they all exhibit strong chiroptical responses with high absorption dissymmetry factor (|gabs |) values (0.020 for H2, 0.021 for H3, and 0.021-0.024 for H4).

Benzannulation Reactions: A Case for Perspective Change From Arene Decoration to Arene Construction.

Benzannulation reactions involve construction of a benzene ring from acyclic precursors. This class of reactions offer a versatile and often superior alternative to aromatic substitution for construction of substituted arenes. Selected pioneering and recent reports of various benzannulation reactions are categorised and discussed in this review.

Lewis Acid-Catalyzed 2,3-Dihydrofuran Acetal Ring-Opening Benzannulations toward Functionalized 1-Hydroxycarbazoles.

The development of a Lewis acid-catalyzed, intramolecular ring-opening benzannulation of 5-(indolyl)2,3-dihydrofuran acetals is described. The resulting 1-hydroxycarbazole-2-carboxylates are formed in up to 90% yield in 1 h. The dihydrofuran acetals are readily accessed from the reactions of enol ethers and α-diazo-ß-indolyl-ß-ketoesters. To highlight the method's synthetic utility, a formal total synthesis of murrayafoline A, a bioactive carbazole-containing natural product, was undertaken.

Synthesis and Photophysical Properties of Soluble N-Doped Rubicenes via Ruthenium-Catalyzed Transfer Hydrogenative Benzannulation.

Ruthenium-catalyzed butadiene-mediated benzannulation enabled the first synthesis of 3,10-(di-tert-butyl)rubicene and its N-doped derivatives as well as preliminary studies on their photophysical properties. Unlike the parent rubicene and 3,10-(di-tert-butyl)rubicene, which adopt classical herringbone-type packing motifs in the solid state, the N-doped congener 7 b displayed columnar packing with an alternating co-facial arrangement of aromatic and heteroaromatic substructures.

Hetero-Type Benzannulation Leading to Substituted Benzothio-Phenes.

TiCl4 (or SnCl4)-promoted hetero-type benzannulation reactions using various (2,2-dichlorocyclopropyl)(thiophen-2-yl)methanols proceeded smoothly to produce uniquely substituted 4-chlorobenzothiophenes (five examples). The present approach involves the first distinctive thiophene formation from thiophene cores, in contrast to traditional methods of thiophene formation from benzene cores. The stereocongested (less reactive) Cl position in the obtained 4-chlorobenzothiophenes functioned successfully as the partners of three cross-coupling reactions: (i) a Suzuki-Miyaura cross-couplings using Pd(OAc)2/SPhos/K3PO4 catalysis (seven examples; 63-91%), (ii) a hydroxylation using KOH/Pd(dba)2/tBu-XPhos catalysis (85%), and (iii) a borylation using a B2(pin)2/Pd(dba)2/XPhos/NaOAc catalysis-provided 4-(pin)B-benzothiophene (58%).

Benzannulation through Ruthenium(0)-Catalyzed Transfer Hydrogenative Cycloaddition: Precision Synthesis and Photophysical Characterization of Soluble Diindenoperylenes.

The first application of ruthenium(0)-catalyzed 1,2-dione-diyne [2+2+2] cycloaddition to PAH construction is achieved by the precision synthesis of soluble diindenoperylenes (DIPs), the electronic structures of which were investigated using steady-state absorption and emission, transient absorption, cyclic voltammetry and time-dependent density functional theory.

Negative Charge as a Lens for Concentrating Antiaromaticity: Using a Pentagonal "Defect" and Helicene Strain for Cyclizations.

Incorporation of a five-membered ring into a helicene framework disrupts aromatic conjugation and provides a site for selective deprotonation. The deprotonation creates an anionic cyclopentadienyl unit, switches on conjugation, leads to a >200 nm red-shift in the absorbance spectrum and injects a charge into a helical conjugated π-system without injecting a spin. Structural consequences of deprotonation were revealed via analysis of a monoanionic helicene co-crystallized with {K+ (18-crown-6)(THF)} and {Cs+ 2 (18-crown-6)3 }. UV/Vis-monitoring of these systems shows a time-dependent formation of mono- and dianionic species, and the latter was isolated and crystallographically characterized. The ability of the twisted helicene frame to delocalize the negative charge was probed as a perturbation of aromaticity using NICS scans. Relief of strain, avoidance of antiaromaticity, and increase in charge delocalization assist in the additional dehydrogenative ring closures that yield a new planarized decacyclic dianion.

Toward Möbius and Tubular Cyclopolyarene Nanorings via Arylbutadiyne Macrocycles.

By harnessing a highly efficient metal-catalyzed tandem cycloaddition reaction as the key benzannulation step, a series of cyclopolyarene nanorings of varied sizes are obtained from poly(arylene-butadiynylene) macrocyclic precursors, which can be synthesized relatively conveniently. Interestingly, due to the nonparallel bond connectivity of the repeat unit, unique Möbius topology is manifested by the cyclopolyarene nanorings composed of an odd number of repeat units, whereas cylindrical tubular structures with radial conjugation are formed with those consisting of an even number of repeat units.

Tetrabenzononacene: "Butterfly Wings" Stabilize the Core.

In combination with bulky substituents at the core, fourfold benzannulation at the cata-positions stabilizes a nonacene sufficiently to allow its isolation and characterization by 1 H NMR and X-ray analysis. The four benzo units blueshift the absorption spectrum in comparison to a solely linear nonacene, but significantly increase the stability in the solid state.

Synthesis, Structure, Photophysical Properties, and Photostability of Benzodipyrenes.

This work explores the syntheses, structures, photophysical properties, and photostability of benzodipyrenes (BDPs). BDPs were synthesized through an InCl3 -AgNTf2 -catalyzed, four-fold alkyne benzannulation reaction. The structures of BDP 4 a and its corresponding endoperoxide product were unambiguously confirmed by X-ray crystallography. The BDPs reported here can also be recognized as peri- and cata-benzannulated pentacenes with a non-functionalized central ring. Unlike the previous reported pentacene-based polycyclic aromatic hydrocarbons, the absorbances of the BDPs were blueshifted by ca. 40 nm relative to pentacene, even after extension of π-conjugation. The newly synthesized BDP products exhibit relatively good stability with half-lives as high as 4612 min in THF.

Triple Helical Ir(ppy)3 Phenylene Cage Prepared by Diol-Mediated Benzannulation: Synthesis, Resolution, Absolute Stereochemistry and Photophysical Properties.

Cyclometalation of a triple helical N-doped phenylene cage prepared by ruthenium(0)-catalyzed diol-diene benzannulation delivers a chiral, conformationally constrained Ir(ppy)3 analogue. Like the parent complex, fac-Ir(ppy)3 , the iridium-containing PAH-cage is phosphorescent, but displays enhanced resistance to oxygen quenching.

Sequential Annulations to Interesting Novel Pyrrolo[3,2-c]carbazoles.

Herein we report a significant, valuable extension of a recently implemented pyrrole benzannulation methodology that, employing versatile nitrodienes from our lab as useful C4 building blocks, led to indole derivatives characterized by unusual patterns of substitution. The 6-nitro-7-arylindoles resulting from suitably derivatized, non-symmetric dienes are of foreseeable synthetic interest in search for new polyheterocyclic systems. As an example, pyrrolocarbazoles with a rarely reported ring fusion were synthesized with the classical Cadogan protocol. Furthermore, the proven easy reducibility of the nitro group to amine will surely open the way to further interesting elaborations.

Total Syntheses of Xiamycins†A, C, F, H and Oridamycin†A and Preliminary Evaluation of their Anti-Fungal Properties.

Divergent and enantiospecific total syntheses of the indolosesquiterpenoids xiamycins A, C, F, H and oridamycin A have been accomplished. The syntheses, which commence from (R)-carvone, employ a key photoinduced benzannulation sequence to forge the carbazole moiety characteristic of these natural products. Late-stage diversification from a common intermediate enabled the first syntheses of xiamycins C and F, and an unexpected one-pot oxidative decarboxylation, which may prove general, led to xiamycin H. All synthetic intermediates and the natural products were tested for anti-fungal activity. Xiamycin H emerged as an inhibitor of three agriculturally relevant fungal pathogens.

Stabilization by Benzannulation: Butterfly Azaacenes.

Soluble butterfly-shaped tetraazapentacenes and tetraazaheptacenes were prepared by condensation or Stille coupling with a stannafluorene. The stability of the benzo-winged tetraazaheptacene is dramatically increased through the fourfold benzannulation, yet its acene character is retained to a significant extent.

"Butterfly Wings" Stabilize Heptacene.

The synthesis of bisalkynylated derivatives of tetrabenzo[a,c,p,r]heptacene and tetrabenzo[a,c,l,n]pentacene via two-/fourfold Stille reactions involving a 9-stannafluorene and suitable tetrabromoacenes is reported. These triphenylene-"winged" heptacenes are surprisingly stable and maintain a significant portion of the electronic properties of heptacenes.

Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations.

The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as graphene nanoribbon synthesis along with a brief discussion of the interesting physical properties these molecules display.