Arenium cation or radical cation? An insight into the cyclodehydrogenation reaction of 2-substituted binaphthyls mediated by Lewis acids

A Generic Platform for Upcycling Polystyrene to Aryl Ketones and Organosulfur Compounds

Polystyrene (PS) is one of the least recycled large-volume commodity plastics due to bulkiness of foam products and associated contaminants. PS recycling is also severely hampered by the lack of financial incentive, limited versatility, and poor selectivity of existing methods. To this end, herein we report a thermochemical recycling strategy of "degradation-upcycling" to synthesize a library of high-value aromatic chemicals from PS wastes with high versatility and selectivity. Two cascade reactions are selected to first degrade PS to benzene under mild temperatures, followed by the derivatization thereof utilizing a variety of acyl/alkyl and sulfinyl chloride additives. To demonstrate the versatility, nine ketones and sulfides of cosmetic and pharmaceutical relevance were prepared, including propiophenone, benzophenone, and diphenyl sulfide. The approach is also amenable to sophisticated upcycling reaction designs and can produce desired products stepwise. The facile and versatile approach will provide a scalable and profitable methodology for upcycling PS waste into value-added chemicals.

1-Substituted Perylene Derivatives by Anionic Cyclodehydrogenation: Analysis of the Reaction Mechanism

Perylene derivatives constitute a promising class of compounds with technological applications mainly due to their optoelectronic properties. One mechanism proposed to synthesize them, starting from binaphthyl derivatives, is anionic cyclodehydrogenation (under reductive conditions). However, the scope of this reaction is limited. In the present study, we report a theoretical and experimental analysis of this particular reaction mechanism for its use in the synthesis of 1-substituted perylenes. Different substituents at position 2 of 1,1'-binaphthalene were evaluated: -OCH₃, -OSi(CH₃)₂C(CH₃)₃, and -N(CH₃)₂. Based on density functional theory (DFT) calculations on the proposed mechanism, we suggest that the cyclization takes place from binaphthyl dianion instead of its radical anion. This dianion has an open-shell diradical nature, and this could be the species that was detected by EPR in previous studies. The O-substituted derivatives could not afford the perylene derivatives since their radical anions fragment and the necessary binaphthyl dianion could not be formed. On the other hand, 49% of N,N-dimethylperylen-1-amine was obtained starting from the N-substituted 2-binapthyl derivative as a substrate, employing a simpler experimental methodology.

Synthesis of Distorted Nitrogen-Doped Nanographenes by Partially Oxidative Cyclodehydrogenation Reaction

A series of partially fused N-doped nanographenes are synthesized via the oxidative cyclodehydrogenation of oligoaryl-substituted dibenzo[ e,l ]pyrene ( 1 ), including compounds ( 2 - 4 ) with five, six, and seven new C-C bonds are formed, respectively, implying stepwise C-C bond fusion and extended π-conjugation. Single-crystal X-ray diffraction analysis of compound 4a revealed that the presence of sterically demanding groups hindered the formation of planar and fully fused nanographene in the oxidative cyclodehydrogenation reaction step. Optical study of compounds 2 to 4 showed that extended π-conjugation leads to a regular stepwise bathochromic shift in the absorption and emission spectra. Furthermore, the HOMO-LUMO gaps of these compounds exhibit a decrease as C-C bond formation proceeds. Thus, the optoelectronic properties of nanographenes are highly dependent on the formation of new C-C bonds in the molecular skeleton.

Synthesis, Structure, and Photophysical Properties of BN-Embedded Analogue of Coronene

Two BN-embedded benzo[ghi]perylene (Bzp) and coronene derivatives (BN-Bzp and BN-Cor) have been successfully synthesized from binaphthyl precursors by new efficient one-pot-multibond routes, and their single crystal structures were analyzed. Both experimental spectra and DFT theoretical calculations indicated that the absorption and emission of these BN-embedded polycyclic aromatic hydrocarbons are significantly enhanced comparing with those of their all carbon analogues. Especially, the fluorescence quantum yield of BN-Cor is nearly 20 times higher than that of ordinary coronene.

Scholl reaction as a powerful tool for the synthesis of nanographenes: a systematic review

Nanographenes, or extended polycyclic aromatic hydrocarbons, have been attracting increasing attention owing to their widespread applications in organic electronics. However, the atomically precise fabrication of nanographenes has thus far been achieved only through synthetic organic chemistry. Polycyclic aromatic hydrocarbons (PAHs) are popular research subjects due to their high stability, rigid planar structure, and characteristic optical spectra. The recent discovery of graphene, which can be regarded as giant PAH, has further stimulated research interest in this area. Chemists working with nanographene and heterocyclic analogs thereof have chosen it as their preferred tool for the assembly of large and complex architectures. The Scholl reaction has maintained significant relevance in contemporary organic synthesis with many advances in recent years and now ranks among the most useful C-C bond-forming processes for the generation of the π-conjugated frameworks of nanographene or their heterocyclic analogs. A broad range of oxidants and Lewis acids have found use in Scholl-type processes, including Cu(OTf)2/AlCl3, FeCl3, MoCl5, PIFA/BF3-Et2O, and DDQ, in combination with Brønsted or Lewis acids, and the surface-mediated reaction has found especially wide applications in PAH synthesis. Undoubtedly, the utility of the Scholl reaction is supreme in the construction of nanographene and their heterocyclic analogues. The detailed analysis of the progress achieved in this field reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted cyclodehydrogenation and developing new reagents. In this review, we highlight and discuss the recent modifications in the Scholl reaction for nanographene synthesis using numerous oxidant systems. In addition, the merits or demerits of each oxidative reagent is described herein.