Palladium-Catalyzed Annulation of o-Iodobiphenyls with o-Bromobenzyl Alcohols: Synthesis of Functionalized Triphenylenes via C–C and C–H Bond Cleavages

Palladium-Catalyzed Annulation Reaction of Bay-Diiodinated Arenes with o-Chloroaromatic Carboxylic Acids to Access Polycyclic Aromatic Compounds

A palladium-catalyzed annulation reaction of bay-diiodinated arenes with o-chloroaromatic carboxylic acids was established. This approach enables the synthesis of a variety of polycyclic aromatic compounds, especially polyalkoxy-substituted polycyclic aromatic compounds, frequently found in discotic liquid-crystalline materials. The investigations indicate that the product 2,3,8,9,12,13-hexakis(hexyloxy)-5-azadibenzo[fg,op]tetracene demonstrates favorable room-temperature liquid-crystalline properties.

Palladium-Catalyzed Annulative π-Extension of Bay-Iodinated Triphenylenes to Access Polycyclic Aromatic Compounds

A palladium-catalyzed annulative π-extension reaction of bay-iodinated triphenylenes with aryl iodides/o-chloroaromatic carboxylic acids was developed. This approach enabled the synthesis of diverse polycyclic aromatic compounds, including dibenzo[fg,op]tetracenes, azadibenzo[fg,op]tetracenes, and tribenzo[a,g,m]coronenes. Initial studies indicate that the resulting product, 2,3,8,9,14,15-hexakis(decyloxy)tribenzo[a,g,m]coronene, exhibits good liquid-crystalline properties.

Research advances in palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors

Transition-metal-catalysed C-H functionalization has emerged as a powerful approach for the transformation of organic molecules due to its high atom and step economy. Palladium-catalysed intermolecular C-H annulation of aryl halides, especially those involving annulation of a five-membered C,C-palladacycle with coupling reagents, have attracted considerable attention in the past decades. This review summarizes the progress on palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors. Mechanistically, five-membered C,C-palladacycles as intermediates are involved in the majority of reactions.

Decarbonylative/decarboxylative [4 + 2] annulation of phthalic anhydrides and cyclic iodoniums towards triphenylenes

A palladium-catalyzed decarbonylative/decarboxylative [4 + 2] annulation of phthalic anhydrides with cyclic diaryliodonium salts to synthesize triphenylenes has been developed. The reaction shows broad substrate scope with a high yield of up to 99%, and it provides an efficient and fast way to access functionalized triphenylenes in only one hour.

Palladium-catalyzed annulative π-extension of o-halobiphenyls with o-chloropyridinecarboxylic acids to access azatriphenylenes

A palladium-catalyzed bay-region annulative π-extension reaction of o-halobiphenyls with o-chloropyridinecarboxylic acids was developed. A variety of azatriphenylene derivatives could be synthesized by this approach.

Transition metal-catalyzed arylation of unstrained C-C single bonds

Carbon-carbon bond activation is one of the most challenging and important research areas in organic chemistry. Selective C-C bond activation of unstrained substrates is difficult to achieve owing to its inert nature and competitive side reactions, but the ubiquitous presence of C-C bonds in organic molecules makes this transformation attractive and of vital importance. Moreover, transition metal-catalyzed arylation of unstrained C-C single bonds can realize the cleavage of old C-C bonds and introduce important aryl groups into the carbon chain to construct new C-C bonds at the same time, providing a powerful and straightforward method to reconstruct the skeleton of the molecules. In recent years, considerable progress has been made in the area of direct arylation of C-C bonds, and β-C elimination or oxidative addition strategies play key roles in these transformations. This review summarizes recent achievements of transition metal-catalyzed arylation of unstrained C-C bonds, demonstrated by various kinds of substrates including alcohol, nitrile and carbonyl compounds, and each example is detailed by its corresponding mechanism, catalytic system and scope of the substrate.

Palladium-catalyzed coupling reaction of 2-iodobiphenyls with alkenyl bromides for the construction of 9-(diorganomethylidene)fluorenes

An atom economical protocol for the construction of 9-(diorganomethylidene)fluorenes through palladium-catalyzed coupling reactions of 2-iodobiphenyls with alkenyl bromides has been reported. The reaction proceeds through the C-H activation/oxidative addition/reduction elimination/intramolecular Heck coupling reaction to afford a series of 9-(diorganomethylidene)fluorenes with good yields. Control experiments demonstrate that a five-membered palladacycle acts as a key intermediate and β-H elimination serves as the rate-limiting step.

Bay-Region Annulative π-Extension of o-Iodobiphenyls with Aliphatic Anhydrides Catalyzed by Pd(OAc)2

Bay-region annulative π-extension of o-iodobiphenyls with aliphatic anhydrides was developed. Many o-iodobiphenyls and aliphatic anhydrides can react well under the optimized conditions. A lot of phenanthrol derivatives can be efficiently prepared by this approach. The control experiments support that dibenzopalladacyclopentadienes may be the reaction intermediates.

α-Bromoacrylic Acids as C1 Insertion Units for Palladium-Catalyzed Decarboxylative Synthesis of Diverse Dibenzofulvenes

Herein α-bromoacrylic acids have been employed as C1 insertion units to achieve the palladium-catalyzed [4 + 1] annulation of 2-iodobiphenyls, which provides an efficient platform for the construction of diverse dibenzofulvenes. This protocol enables the formation of double C(aryl)-C(vinyl) bonds via a C(vinyl)-Br bond cleavage and decarboxylation. It is particularly noteworthy that the method features a broad substrate scope, and various interesting frameworks, such as bridged ring, fused (hetero)aromatic ring, and divinylbenzene, can be successfully incorporated into the products.

Cu-Catalyzed Aromatic Metamorphosis of 3-Aminoindazoles

We present a novel Cu-catalyzed aromatic metamorphosis of 3-aminoindazoles via oxidative cleavage of two C-N bonds of 3-aminoindazoles. This unprecedented reactivity of 3-aminoindazoles allows one to forge diverse nitrile-containing triphenylenes in decent yields via generation of the cyano group in situ. The current study reveals that 3-aminoindazoles could be harnessed as radical precursors via oxidative denitrogenation, the reaction mechanism of which was supported by density functional theory calculations.

A Synthetic Strategy for the Construction of Functionalized Triphenylene Frameworks via Palladium Catalyzed Intramolecular Annulation/Decyanogenative C-H Bond Alkenylation

The palladium catalyzed synthesis of 14-phenylbenzo[ f]tetraphene-9-carbonitrile derivatives as core polycyclic aromatic hydrocarbons (PAHs) was achieved via an intramolecular annulation and decyanogenative C-H bond alkenylation strategy. A readily synthesized Knoevenagel condensation product of [1,1'-biphenyl]-2,2'-dicarbaldehyde with benzyl cyanide converted successfully into 14-phenylbenzo[ f]tetraphene-9-carbonitrile derivatives in excellent yields up to 94%. The transformation involves an intramolecular cascade C-C bond formation along with a C-H bond cleavage sequence.

Palladium-catalyzed successive C–H bond arylations and annulations toward the π-extension of selenophene-containing aromatic skeletons

A modular approach for the synthesis of planar π-extended selenium containing molecules from selenophene has been developed.

Catalytic activations of unstrained C–C bond involving organometallic intermediates

In this review, the transition-metal-catalyzed C–C bond activation of relatively stable and unstrained molecules involving organometallic intermediates is discussed in detail.

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

An amine-triggered facile synthetic approach of anthranilates has been described through benzannulation of readily available chemicals under one-pot solvent-free conditions using Ca(OTf)₂ as the sustainable catalyst. In this regioselective approach, we described a reasonably longer cascade, which proceeds through β-enamino ester formation/Michael addition/intramolecular aldol reaction/elimination/aromatization/oxidative debenzylation/lactonization with a broad substrate scope and high yields. The isolation of intermediates authenticated the mechanism, and the synthetic utility of the products was also demonstrated.

Synthesis of substituted oxazoles via Pd-catalyzed tandem oxidative cyclization

An easy approach to access multisubstituted oxazoles via tandem oxidative cyclization is developed.

Three-Step Synthesis of Fluoranthenes through Pd-Catalyzed Inter- and Intramolecular C-H Arylation

A three-step synthetic method for the preparation of fluoranthenes, involving Miura's intermolecular C-H arylation, nonaflation, and intramolecular C-H arylation, has been developed. Various 1-naphthols and haloarenes were successfully used as substrates. Reaction conditions that afford high site selectivity have been developed for the intramolecular C-H arylation step.

Synthesis, structure and properties of polysubstituted benzo[g]chrysene by FeCl3-promoted from diphenylacetypene and phenylacetaldehyde derivatives

Benzo[g]chrysene (BgCh) is a new untapped virgin land in PAHs. A new and straightforward method has been developed to synthesize it. Part of BgCh revealed liquid crystalline properties and their fluorescence emission wavelength is in the range of blue light.