Base‐Selective Five‐ versus Six‐Membered Ring Annulation in Palladium‐Catalyzed C–C Coupling Cascade Reactions: New Access to Electron‐Poor Polycyclic Aromatic Dicarboximides

Palladium‐catalyzed base‐selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross‐coupling and direct C−H arylation afforded a series of new five‐ and six‐membered ring annulated electron‐poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs₂CO₃) as auxiliary base in these C−C coupling cascade reactions led exclusively to six‐membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five‐membered ring annulated products. This base‐dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X‐ray analysis of the respective five‐ and six‐membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry.     

Tandem Regioselective Substitution and Palladium‐Catalyzed Ring Fusion Reaction for Core‐Expanded Boron Dipyrromethenes with Red‐Shifted Absorption and Intense Fluorescence

A selective method for the core‐extension of boron dipyrromethene (BODIPY) with two annulated indole rings with exclusive syn‐connectivity is reported. The method is based on a regioselective nucleophilic substitution reaction of 2,3,5,6‐tetrabromoBODIPY with aryl amines, followed by palladium‐catalyzed intramolecular C?C coupling ring fusion. The unsymmetrical core‐expanded BODIPY with annulated indole and benzofuran rings was also synthesized by stepwise and regioselective nucleophilic substitution and palladium‐catalyzed intramolecular C?C coupling reaction. The diindole‐annulated BODIPY was unambiguously characterized by single‐crystal X‐ray analysis. The optical properties of the present core‐expanded BODIPYs were studied, revealing clearly red‐shifted absorption and emission bands and enhanced absorption coefficients upon annulation.     

Exfoliation of Graphite into Graphene in Polar Solvents Mediated by Amphiphilic Hexa‐peri‐hexabenzocoronene

A water‐soluble surfactant consisting of hexa‐peri‐hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self‐assembled nanofiber structure in the solid state. Profiting from the π interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mg L^?1 containing 2–6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100–500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements.     

Zirconacyclopentadiene‐Annulated Polycyclic Aromatic Hydrocarbons

Syntheses of large polycyclic aromatic hydrocarbons (PAHs) and graphene nanostructures demand methods that are capable of selectively and efficiently fusing large numbers of aromatic rings, yet such methods remain scarce. Herein, we report a new approach that is based on the quantitative intramolecular reductive cyclization of an oligo(diyne) with a low‐valent zirconocene reagent, which gives a PAH with one or more annulated zirconacyclopentadienes (ZrPAHs). The efficiency of this process is demonstrated by a high‐yielding fivefold intramolecular coupling to form a helical ZrPAH with 16 fused rings (from a precursor with no fused rings). Several other PAH topologies are also reported. Protodemetalation of the ZrPAHs allowed full characterization (including by X‐ray crystallography) of PAHs containing one or more appended dienes with the ortho‐quinodimethane (o‐QDM) structure, which are usually too reactive for isolation and are potentially valuable for the fusion of additional rings by Diels–Alder reactions.     

Bay‐Annulated Perylene Tetraesters: A New Class of Discotic Liquid Crystals

Selenium‐annulated perylene tetraesters that stabilize the hexagonal columnar phase have been synthesized and characterized, and their thermal and photophysical behavior has been determined. The mesophase range decreased with an increase in chain length. A comparative account of the structure–property relationships of this series of compounds with respect to parent perylene tetraesters, N‐ and S‐annulated perylene tetraesters, in terms of their thermal, photophysical and electrochemical behavior is provided. The bay‐annulation of perylene tetraesters is a good option to modify the thermal and photophysical properties of perylene derivatives and it can provide a new avenue for the synthesis of several technologically important self‐assembling perylene derivatives.     

Controllable Sulfur,Nitrogen Co‐doped Porous Carbon for Ethylbenzene Oxidation: The Role of Nano‐CaCO3

Heteroatom‐doped porous carbon materials have exhibited promising applications in various fields. In this work, sulfur, nitrogen co‐doped carbon materials (SNCs) with abundant pore structure were prepared by pyrolysis of sulfur, nitrogen‐containing porous organic polymers (POPs) mixed with nano‐CaCO₃ at high temperature. Among the resultant materials, SNC‐Ca‐850 possesses a relatively high level of doped heteroatoms and exhibits an excellent catalytic performance for the selective oxidation of benzylic C?H bonds. It is noteworthy that nano‐CaCO₃ increases the doped sulfur content in the synthesized carbon materials to a large extent and impacts the existence modes of sulfur. In addition, it enhances the porous structure and specific surface area of the resultant SNCs significantly. This work provides a viable strategy to promote the doping of sulfur into carbon materials during the pyrolysis process.     

Base-Selective Five- versus Six-Membered Ring Annulation in Palladium-Catalyzed C–C Coupling Cascade Reactions: New Access to Electron-Poor Polycyclic Aromatic Dicarboximides

Palladium-catalyzed base-selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross-coupling and direct C−H arylation afforded a series of new five- and six-membered ring annulated electron-poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs₂CO₃) as auxiliary base in these C−C coupling cascade reactions led exclusively to six-membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five-membered ring annulated products. This base-dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X-ray analysis of the respective five- and six-membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry.     

Intrinsically Sulfur‐ and Nitrogen‐Co‐doped Carbons from Thiazolium Salts

Carbon materials that are intrinsically co‐doped with nitrogen and sulfur heteroatoms are synthesised by facile annealing of nitrile‐functionalised thiazolium salts. Extremely high degrees of doping are achieved, especially for sulfur. The method further allows for direct tuning of the amounts of both N and S, establishing a new synthetic pathway in the emerging field of S‐doped carbon materials.     

Aromatic Homologation by Non‐Chelate‐Assisted RhIII‐Catalyzed CH Functionalization of Arenes with Alkynes

Larger condensed arenes are of interest owing to their electro‐ and photochemical properties. An efficient synthesis is the catalyzed aromatic annulation of a smaller arene with two alkyne molecules. Besides difunctionalized starting materials, directed C? H functionalization can be used for such aromatic homologation. However, thus far the requirement of either pre‐functionalized substrates or suitable directing groups were limiting this approach. Herein, we describe a rhodium(III)‐catalyzed method allowing the use of completely unbiased arenes and internal alkynes. The reaction works best with copper(II) 2‐ethylhexanoate and decabromodiphenyl ether as the oxidant combination. This aromatic annulation tolerates a variety of functional groups and delivers homologated condensed arenes. Aside from simple benzenes, naphthalenes and higher condensed arenes provide access to highly substituted and highly soluble acenes structures having important electronic and photophysical properties.     

Herring‐bone π–π interactions in trans‐2,6‐diphenyl‐2,3,5,6‐tetrahydrothiapyran‐4‐one

The structure of the title compound, C₁₇H₁₆OS, is primarily stabilized by T‐shaped and parallel‐displaced aromatic clusters. The distances between the centroids of the aromatic pairs are in the range 4.34–5.30 Å. In the crystal packing, the mol­ecules dimerize by means of π–π interactions of both face‐to‐face and edge‐to‐face types, and the aromatic rings associate in a cyclic edge‐to‐face tetrameric arrangement of the herring‐bone type. These herring‐bone interactions appear to insulate hydrogen‐bond interactions in the crystal structure.     

Aromatic Homologation by Non‐Chelate‐Assisted RhIII‐Catalyzed C?H Functionalization of Arenes with Alkynes

Larger condensed arenes are of interest owing to their electro‐ and photochemical properties. An efficient synthesis is the catalyzed aromatic annulation of a smaller arene with two alkyne molecules. Besides difunctionalized starting materials, directed C H functionalization can be used for such aromatic homologation. However, thus far the requirement of either pre‐functionalized substrates or suitable directing groups were limiting this approach. Herein, we describe a rhodium(III)‐catalyzed method allowing the use of completely unbiased arenes and internal alkynes. The reaction works best with copper(II) 2‐ethylhexanoate and decabromodiphenyl ether as the oxidant combination. This aromatic annulation tolerates a variety of functional groups and delivers homologated condensed arenes. Aside from simple benzenes, naphthalenes and higher condensed arenes provide access to highly substituted and highly soluble acenes structures having important electronic and photophysical properties.     

Skeletal Rearrangement of Twisted Thia‐Norhexaphyrin: Multiply Annulated Polypyrrolic Aromatic Macrocycles

A hybrid thia‐norhexaphyrin comprising a directly linked N‐confused pyrrole and thiophene unit ( 1 ) revealed unique macrocycle transformations to afford multiply inner‐annulated aromatic macrocycles. Oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone triggered a cleavage of the C?S bond of the thiophene unit, accompanied with skeletal rearrangement to afford unique π‐conjugated products: a thiopyrrolo‐pentaphyrin embedded with a pyrrolo[1,2]isothiazole ( 2 ), a sulfur‐free pentaphyrin incorporating an indolizine moiety ( 3 ), and a thiopyranyltriphyrinoid containing a 2H‐thiopyran unit ( 4 ). Furthermore, 2 underwent desulfurization reactions to afford a fused pentaphyrin containing a pyrrolizine moiety ( 5 ) under mild conditions. Using expanded porphyrin scaffolds, oxidative thiophene cleavage and desulfurization of the hitherto unknown N‐confused core‐modified macrocycles would be a practical approach for developing unique polypyrrolic aromatic macrocycles.     

A Large π‐Extended Carbon Nanoring Based on Nanographene Units: Bottom‐Up Synthesis,Photophysical Properties,and Selective Complexation with Fullerene C70

Herein we report the organoplatinum‐mediated bottom‐up synthesis, characterization, and properties of a novel large π‐extended carbon nanoring based on a nanographene hexa‐peri ‐hexabenzocoronene (HBC) building unit. This tubular structure can be considered as an example of the longitudinal extension of the cycloparaphenylene scaffold to form a large π‐extended carbon nanotube (CNT) segment. The cyclic tetramer of a tetramesityl HBC ([4]CHBC) was synthesized by the reaction of a 2,11‐diborylated hexa‐peri ‐hexabenzocoronene with a platinum complex, followed by reductive elimination. The structure of this tubular molecule was further confirmed by physical characterization. Theoretical calculations indicate that the strain energy of this nanoring is as high as 49.18 kcal mol⁻¹. The selective supramolecular host–guest interaction between [4]CHBC and C₇₀ was also investigated.     

A Large π‐Extended Carbon Nanoring Based on Nanographene Units: Bottom‐Up Synthesis,Photophysical Properties,and Selective Complexation with Fullerene C70

Herein we report the organoplatinum‐mediated bottom‐up synthesis, characterization, and properties of a novel large π‐extended carbon nanoring based on a nanographene hexa‐peri ‐hexabenzocoronene (HBC) building unit. This tubular structure can be considered as an example of the longitudinal extension of the cycloparaphenylene scaffold to form a large π‐extended carbon nanotube (CNT) segment. The cyclic tetramer of a tetramesityl HBC ([4]CHBC) was synthesized by the reaction of a 2,11‐diborylated hexa‐peri ‐hexabenzocoronene with a platinum complex, followed by reductive elimination. The structure of this tubular molecule was further confirmed by physical characterization. Theoretical calculations indicate that the strain energy of this nanoring is as high as 49.18 kcal mol⁻¹. The selective supramolecular host–guest interaction between [4]CHBC and C₇₀ was also investigated.     

Palladium‐Catalyzed Annulation of 9‐Halophenanthrenes with Alkynes: Synthesis,Structural Analysis,and Properties of Acephenanthrylene‐Based Derivatives

The palladium‐catalyzed annulation of 9‐bromo‐ and 9‐chlorophenanthrenes with alkynes gave 4,5‐disubstituted acephenanthrylenes in yields of 58–95 % (9 examples). Asymmetric alkynes, such as 1‐phenyl‐1‐propyne, 1‐phenyl‐1‐hexyne, and 1‐cyclopropyl‐2‐phenylethyne, regioselectively form (cyclo)alkyl‐substituted products, following the regular rule that governs the carbopalladation of alkynes. This synthetic protocol can also be utilized in annulations with several π‐extended bromoarenes, such as 7‐bromo[5]helicene, 5‐bromo[4]helicene, 9‐bromoanthracene, 3‐bromoperylene, and 3‐bromofluoranthene, to give the corresponding annulated products in moderate to good yields (51–86 %; 6 examples). Similarly, bromocorannulene produced highly curved 1,2‐disubstituted cyclopentacorannulenes. Reactions of 6,12‐dibromochrysene and 4,7‐dibromo[4]helicene with di(4‐tolyl)ethyne provided the twofold annulated products in moderate yields. 4,5‐Diphenylacephenanthrylene and 6,7‐diphenylbenzo[a]acephenanthrylene thus generated were converted into phenanthro[9,10‐e]acephenanthrylene and benzo[a]phenanthro[9,10‐e]acephenanthrylene, respectively, by oxidative cyclodehydrogenation. The structures of 4,5‐diphenylacephenanthrylene, 4,5‐diphenyldibenzo[a,l]acephenanthrylene, 1,2‐diarylcyclopentacorannulenes, and benzo[a]phenanthro[9,10‐e]acephenanthrylene were verified by X‐ray crystallography. The photophysical and electrochemical properties of the selected annulated products were investigated.     

Unexpected Michael Additions on the Way to 2.3,8.9‐Dibenzanthanthrenes with Interesting Structural Properties

The synthesis and properties of a new polycyclic aromatic hydrocarbon containing eight annulated rings and based on the anthanthrene core is described. An unexpected, nucleophile‐dependent Michael addition to a dibenzanthanthrene‐1,7‐dione is found, giving a product with three triisopropylsilylacetylene units and a remarkable solid‐state structure (as determined by X‐ray crystallography).     

Radical Mediated Aza‐Pauson‐Khand Reaction of Acetylenes,Imines, and CO Leading to Five‐Membered Unsaturated Lactams

Formal [2+2+1] cycloaddition reaction involving acetylenes, aromatic imines, and CO was achieved by radical chain reaction, which gave five‐membered unsaturated lactams in modest to good yields. When we used 5‐chloropentyne, sequential carbonylation took place accompanied with double annulation events to give a cyclohexanone‐fused lactam in excellent stereoselectivity.     

Visible‐Light‐Driven Photocatalytic Activation of Inert Sulfur Ylides for 3‐Acyl Oxindole Synthesis

Bicarbonyl‐substituted sulfur ylide is a useful, but inert reagent in organic synthesis. Usually, harsh reaction conditions are required for its transformation. For the first time, it was demonstrated that a new, visible‐light photoredox catalytic annulation of sulfur ylides under extremely mild conditions, permits the synthesis of oxindole derivatives in high selectivities and efficiencies. The key to its success is the photocatalytic single‐electron‐transfer (SET) oxidation of the inert amide and acyl‐stabilized sulfur ylides to reactive radical cations, which easily proceeds with intramolecular C?H functionalization to give the final products.     

X‐Shaped Polycyclic Aromatic Hydrocarbons: Optical Properties and Tunable Assembly Ability

Although a number of synthetic methodologies have been developed to prepare stable polycyclic aromatic hydrocarbons (PAHs), much less research has been devoted to functionalizing the peripheries of molecules to tune the self‐assembly ability or introduce functional groups without altering their photophysical properties. Herein, we report twisted “X”‐shaped molecules prepared through annulation of hexacene with benzoanthracene on the zigzag edge, and an investigation of their photophysical properties and self‐assembly properties. The shape‐complementary “X”‐shaped molecules prefer to dimerize, while the π‐extension would lead to one‐dimensional π‐stacking. Our findings give some insights into the design of stable PAHs without disturbing the electronic structures.     

A Noncatalytic Approach to Hetaryl‐Annulated 1,2,4‐Thiadiazine‐1,1‐dioxides

A set of synthetic procedures was developed to yield functionalized pyrido‐, pyrimido‐, and thiazo‐annulated thiadiazine‐1,1‐dioxides on a preparative scale. In all cases the thiadiazine‐1,1‐dioxide ring closure was carried out through a reaction of hetaryl‐sulfonyl chlorides with amidines under mild noncatalytic conditions. In the case of 2‐chloropyridine‐3‐sulfonyl chloride derivatives and 2,4‐dichlorothiazole‐5‐sulfonyl chloride open‐chain sulfonylated amidine intermediates were isolated and then subjected to the cyclization step. The reaction with 2,4‐dichloropyrimidine‐5‐sulfonyl chloride gave rise to the corresponding thiadiazine‐1,1‐dioxides in one‐pot. Similarly, a reaction of 2‐chloropyridine‐3‐sulfonamide with lactime ethers proceeded in one‐pot readily giving the corresponding thiadiazine‐1,1‐dioxides. Remaining chlorine atoms on the prepared hetaryl‐annulated benzothiadiazine‐1,1‐dioxides readily undergo aromatic nucleophilic displacement reactions serving thus as additional variation points for the design of biologically potent compounds.