Brønsted Acid Mediated Synthesis and Properties of Dibenzoacridine Derivatives

Synthesis and Properties of 5-Azaullazines

5-Azaullazines, indolizino[6,5,4,3-ija][1,5]naphthyridines, and their benzo-fused analogues were prepared in three steps by combination of Pd catalyzed cross-coupling reactions with Brønsted acid mediated cycloisomerisations. The reaction tolerates various substitution patterns and functional groups and proceeds in high yields. Optical and electrochemical properties of selected products were studied experimentally and by DFT calculations.

Synthesis and Properties of Diphenylbenzo[j]naphtho[2,1,8-def][2,7]phenanthrolines

A series of hitherto unknown 5,14-diphenylbenzo[j]naphtho[2,1,8-def][2,7]phenanthrolines, containing a 5-azatetracene and a 2-azapyrene subunit, were prepared by combination of Pd-catalyzed cross-coupling reactions with a one-pot Povarov/cycloisomerization reaction. In the final key step four new bonds are formed in one step. The synthetic approach allows for a high degree of diversification of the heterocyclic core structure. The optical and electrochemical properties were studied experimentally and by DFT/TD-DFT and NICS calculations. Due to the presence of the 2-azapyrene subunit, the typical electronic nature and characteristics of the 5-azatetracene moiety are lost and the compounds are electronically and optically more related to 2-azapyrenes.

Photoredox-Catalyzed Cascade sp2 C-H Bond Functionalization to Construct Substituted Acridine with Diarylamine and Hypervalent Iodine(III) Reagents

A photocatalyzed cascade double C-C formation via sp² C-H bond activation of diarylamines with hypervalent iodine diazo reagents was developed. A variety of diarylamines and hypervalent iodine(III) reagents were tolerated well, and a range of substituted acridines with yields ranging from moderate to excellent was provided efficiently. The protocol introduces diazo groups onto diarylamines and enables subsequent late-stage assembly point functionalization with the diazonium structure, forming two new C-C bonds in a sequential fashion.

Synthesis of Nitrogen Heterocycles by a C–C Cross-Coupling/Cycloisomerization Strategy

The present article presents a personalized Account on the synthesis of nitrogen heterocycles by combination of regioselective Pd-catalyzed cross-coupling reactions of polyhalogenated heterocycles, i.e., Suzuki–Miyaura and Sonogashira reactions, with acid-mediated cycloisomerization reactions. In many cases, the products constitute new heterocyclic core structures and show interesting optical and electronic properties.

1 Introduction

2 Acridines

3 Phenathridines

4 Azapyrenes

5 Thienoquinolines

6 Pyrrolonaphthyridines

7 6-Aza-ullazines

8 Conclusions

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

A facile synthesis of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridine derivatives is reported which is based on POCl₃-mediated cyclodehydration followed by double Suzuki-Miyaura cross-coupling. The absorption and fluorescence properties of the obtained products were investigated and their HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. Besides, density functional theory calculations were carried out for further exploration of their electronic properties.

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

Acridine derivatives have attracted considerable interest in numerous areas owing to their attractive physical and chemical properties. Herein, starting from readily available anthranilic acid, an efficient synthesis of 2,4-bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridine derivatives was accomplished via a one-pot double Sonogashira cross-coupling method. The UV-visible absorption and emission properties of the synthesized molecules have been examined. Additionally, theoretical studies based on density functional theory (DFT/B3LYP/6-31G(d)) were carried out.

Synthesis of Pyrrolo[1,2-a][1,6]- and [1,8]naphthyridines by Alkyne-Carbonyl Metathesis

A concise and modular synthesis of pyrrolo[1,2-a][1,6]- and [1,8]naphthyridines by a one-pot two-step reaction consisting of electrophilic acylation followed by an alkyne-carbonyl-metathesis reaction as the final cyclization step is reported. This developed synthetic methodology allows the facile synthesis of these heterocyclic core structures in mainly high overall yields under metal-free conditions. Reaction conditions are carefully optimized and display a novel supplement to access these tricyclic heterocyclic compounds.

Scandium(III) Triflate-Catalyzed Reaction of Aroyl-Substituted Donor-Acceptor Cyclopropanes with 1-Naphthylamines: Access to Dibenzo[c,h]acridines

The reaction of aroyl-substituted donor-acceptor (D-A) cyclopropanes with two equivalents of 1-naphthylamines in the presence of a catalytic amount of scandium(III) triflate provides access to dibenzo[c,h]acridines. The key steps of the transformation are the formation of nucleophilic ring-opening products from the D-A cyclopropanes and 1-naphthylamines and their subsequent fragmentation and cyclization. The method has a reasonable substrate scope, and the products are formed in 50-70% yields.

Acid-promoted synthesis and photophysical properties of substituted acridine derivatives

A simple and efficient synthetic protocol for the preparation of acridinium esters and amides through the cyclization and esterification or amidation of isatins with alcohols or amines as nucleophiles in the presence of CF3SO3H is established. A series of polycyclic acridine derivatives bearing large π-conjugated systems were obtained in high yields, including some key intermediates for the synthesis of biologically active molecules. The photophysical properties of these synthesized acridines were investigated, demonstrating that the sulfur heterocyclic acridine 9w was obtained in a high quantum yield.

Synthesis of 2-Azapyrenes and Their Photophysical and Electrochemical Properties

A series of 5,7,9-substituted 2-azapyrenes were synthesized for the first time. The synthesis relies on Brønsted acid promoted benzannulation of alkyne precursors prepared by palladium-catalyzed cross-coupling reactions. The synthetic strategy is efficient and the scope covers a variety of functional groups. The electrochemical behavior and photophysical properties of the products were investigated by UV-vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations.

Synthesis of thieno[2,3-h]-/[3,2-h]quinolines and thieno[2,3-f] quinolines by Brønsted acid mediated cycloisomerisation

Several thieno[2,3-h]-/[3,2-h]- and [2,3-f]quinolines have been synthesised from 2,3-dihalogenated pyridines or -quinolines by site-selective Pd catalysed cross-coupling reactions and Brønsted acid mediated cycloisomerisations as the final key step. This newly developed synthetic strategy is used in a modular way to synthesize diverse regioisomeric derivatives, tolerates various functional groups, and proceeds with high selectivity, and the desired final products have been isolated in high overall yields.

Application of the Povarov Reaction in Biaryls under Iron Catalysis for the General Synthesis of Dibenzo[a,c]Acridines

A modified Povarov reaction involving 2'-alkynylbiaryl-2-carbaldehydes and aryl amines with tandem oxidation was performed using catalytic FeCl₃. The outcome was an efficient general synthesis of dibenzo[a,c]acridines with moderate to high yields. This method offers simplicity in the preparation of substrates, diverse substrate scope, and high atom economy. The generality of the protocol was verified by synthesizing a tribenzo[a,c,h]acridine derivative. Photophysical properties of the synthesized compounds were also studied. The compounds absorb UV light typically in the range 230-330 nm and emit in the visible range of 400-420 nm.