Ultrasound-assisted synthesis of RO- and RS-substituted (hetero)acenes via oxo- and thio-Friedel-Crafts/Bradsher reactions

The First Example of the Friedel-Crafts Cyclization Leading to (10-Hydroxy-9,10-dihydroanthr-9-yl)phosphonium Salts without the Expected Bradsher Dehydration

The reaction of (ortho-acetalaryl)arylmethanols with various phosphines PR1R2R3 (R1 = R2 = R3 = Ph; R1 = R2 = Ph, R3 = Me and R1 = R2 = Me, R3 = Ph) under acidic conditions (e.g., HCl, HBF4, TsOH) unexpectedly led to the formation of (10-hydroxy-9,10-dihydroanthr-9-yl)phosphonium salts instead of the corresponding anthryl phosphonium salts. The cyclization occurred according to the Friedel-Crafts mechanism but without the usually observed Bradsher dehydration, giving cyclic products in the form of cis/trans isomers and their conformers. In case of electron-rich and less-hindered dimethylphenylphosphine, all four stereoisomers were recorded in 31P{1H} NMR spectra, while for the other phosphines, only the two most stable cis/trans stereoisomers were detected. This study was supported by DFT and NCI calculations in combination with FT-IR analysis.

Highly Substituted 10-RO-(hetero)acenes-Electric Properties of Vacuum-Deposited Molecular Films

The functionalization of the aromatic backbone allows the improvement of the electrical properties of acene molecules in the amorphous layered structures of organic thin films. In the present work, we discuss the electric properties of the stable, amorphous, vacuum-deposited films prepared from five highly substituted 10-RO-acenes of various electronic properties, i.e., two extreme electron-donor (1,3-dioxa-cyclopenta[b]) anthracenes with all RO substituents, two anthracene carbaldehydes and one benzo[b]carbazole carbaldehyde possessing both electron-donor and acceptor substituents. The hole mobility data were obtained using subsequent steady state space charge limited currents (SCLC) and Time of Flight (TOF) measurements, performed on the same sample and these were then compared with the results of theoretical hole mobility calculations obtained using the Density Functional Theory (DFT) quantum-chemical calculations using the Marcus-Hush theory. The study shows a good agreement between the theoretical and experimental values which allows for the quick and quantitative estimation of Einstein's mobility values for highly substituted 10-RO anthracene and benzo[b]carbazole based on chemical calculations. This agreement also proves that the transport of holes follows the hopping mechanism. The theoretical calculations indicate that the reorganization energy plays a decisive role in the transport of holes in the amorphous layers of highly substituted hetero(acenes).

O,S-Acetals in a New Modification of oxo-Friedel-Crafts-Bradsher Cyclization-Synthesis of Fluorescent (Hetero)acenes and Mechanistic Considerations

This paper presents the use of O,S-acetals in a new modification of the oxo-Friedel-Crafts-Bradsher cyclization. In this reaction, under mild reaction conditions (25 °C), three- and four-ring fused RO-acenes (major) and/or HO(CH₂)₂S-acenes (minor) are formed, the latter products having never been observed before in this type of cyclization. In this way, two electronically different fluorophores could be obtained in a single cyclization reaction, one of them having strong electron donor properties (+M effect of alkoxy groups) and the other having donor-acceptor properties (+M and -I effects of the HO(CH₂)₂S-group, Hammett's constants). Further increasing the reaction temperature, HCl concentration or prolonging reaction time, surprisingly, yielded a 2:1 mixture of cis and trans dimeric isomers, as the only products of this cyclization. The DFT calculations confirmed a greater stability of the cis isomer compared to the trans isomer. The formation of unexpected dimeric products and HO(CH₂)₂S-acenes sheds light on the mechanism of oxo-Friedel-Crafts-Bradsher cyclization, involving competitive O/S atom protonation in strained O,S-acetals and in strain-free side groups of intermediate species.

Palladium immobilized on guanidine functionalized magnetic nanoparticles: a highly effective and recoverable catalyst for ultrasound aided Suzuki–Miyaura cross-coupling reactions

The Fe3O4@SiO2-TCT-Gua-Pd catalyst anchored with guanidine moiety on Fe3O4 nanoparticles was synthesised for Suzuki–Miyaura cross coupling reaction.

Unconventional approaches for the introduction of sulfur-based functional groups

Organosulfur compounds have a pivotal role in the functionalities of many natural products, pharmaceuticals and organic materials. For these reasons, the search for new methodologies for the formation of carbon-sulfur bonds has been the object of intensive work for organic chemists. However, the proposed strategies suffer from various drawbacks, such as volatility, toxicity, and instability of the sulfur sources or the use of VOC solvents. In this review, we summarise the recent protocols which have the goal of obtaining sulfones, thioethers, thiazines, thiazepines and sulfonamides in an unconventional and/or sustainable way. The use of starting materials less invasive and toxic with respect to the traditional reagents, alternative solvents such as water, ionic liquids or deep eutectic solvents, the exploitation of ultrasound and electrochemistry, increasing the efficiency of the process, are reported. Moreover, representative reaction mechanisms are also discussed.