Beilstein Journal of Organic Chemistry最新文献

The polycyclic skeleton of tris(4,5-dehydro-2,3:6,7-dibenzotropone) is a key structural fragment in carbon schwarzites, a theoretical form of negatively curved carbon allotrope. This report presents a new synthesis of this compound using a Ni-mediated Yamamoto coupling reaction and structural analysis of it with X-ray crystallography. Interestingly, it is observed that tris(4,5-dehydro-2,3:6,7-dibenzotropone) crystallized from its solution in hexane resulting in colorless and yellow crystal polymorphs, where it adopts conformations of approximate C _s and C ₂ symmetry, respectively. Furthermore, expanding its π-skeleton through the Barton-Kellogg and Scholl reactions led to the successful synthesis of a curved polycyclic arene containing three heptagons and two pentagons.

Acenaphthylene-fused heteroarenes with a variety of five- and six-membered heterocycles such as thiophene, furan, benzofuran, pyrazole, pyridine and pyrimidine were synthesized via an efficient Pd-catalyzed reaction cascade in good to high yields (45-90%). This cascade involves an initial Suzuki-Miyaura cross-coupling reaction between 1,8-dihalonaphthalenes and heteroarylboronic acids or esters, followed by an intramolecular C-H arylation under the same conditions to yield the final heterocyclic fluoranthene analogues. The method was further employed to access polyoxygenated benzo[j]fluoranthenes, which are all structurally relevant to benzo[j]fluoranthene-based fungal natural products. The effectiveness of our strategy was demonstrated via a concise, four-step synthesis of the tetramethoxybenzo[j]fluoranthene derivative 18, which represents a formal total synthesis of the fungal natural product bulgarein.

The reactivity of our recently disclosed hypervalent iodine reagents (HIRs) bearing a benzylamine with in situ-generated sulfenate salts was investigated. Under the studied conditions sulfonamides have been obtained in up to 52% yield. This reaction has been extended to a variety of HIRs and sulfenate salts to explore the different reactivity of these new reagents. A plausible mechanism is proposed, suggesting a possible radical pathway.

The rising popularity of bioconjugate therapeutics has led to growing interest in late-stage functionalization (LSF) of peptide scaffolds. α,β-Unsaturated amino acids like dehydroalanine (Dha) derivatives have emerged as particularly useful structures, as the electron-deficient olefin moiety can engage in late-stage functionalization reactions, like a Giese-type reaction. Cheap and widely available building blocks like organohalides can be converted into alkyl radicals by means of photoinduced silane-mediated halogen-atom transfer (XAT) to offer a mild and straightforward methodology of alkylation. In this research, we present a metal-free strategy for the photochemical alkylation of dehydroalanine derivatives. Upon abstraction of a hydride from tris(trimethylsilyl)silane (TTMS) by an excited benzophenone derivative, the formed silane radical can undergo a XAT with an alkyl bromide to generate an alkyl radical. Consequently, the alkyl radical undergoes a Giese-type reaction with the Dha derivative, forming a new C(sp³)-C(sp³) bond. The reaction can be performed in a phosphate-buffered saline (PBS) solution and shows post-functionalization prospects through pathways involving classical peptide chemistry.

The high potential of non-covalent arene-fluoroarene intermolecular interactions in the design of liquid crystals lies in their ability to strongly promote self-assembly, improve the order and stability of the supramolecular mesophases, and enable tuneability of the optical and electronic properties, which can potentially be exploited for advanced applications in display technologies, photonic devices, sensors, and organic electronics. We recently successfully reported the straightforward synthesis of several mesogens containing four lateral aliphatic chains and derived from the classical triphenylene core self-assembling in columnar mesophases based on this paradigm. These mesogenic compounds were simply obtained in good yields by the nucleophilic substitution (S_NFAr) of various types of commercially available fluoroarenes with the electrophilic organolithium derivatives 2,2'-dilithio-4,4',5,5'-tetraalkoxy-1,1'-biphenyl (2Li-BP n). In a continuation of this study, aiming at testing the limits of the reaction and providing a large diversity of structures, a structurally related series of compounds is reported here, namely 1,2,4-trifluoro-6,7,10,11-tetraalkoxy-3-(perfluorophenyl)triphenylenes (F n). They were obtained by reacting the above mentioned 2,2'-dilithiobiphenyl derivatives with decafluorobiphenyl, C₆F₅-C₆F₅. These compounds differ from the previously reported series, 1,2,4-trifluoro-6,7,10,11-tetraalkoxy-3-aryltriphenylenes (PH n), solely by the substitution of the terminal phenyl ring with a pentafluorophenyl ring. Thus, as expected, they display a Col_hex mesophase over large temperature ranges, with only small differences in the mesophase stability and transition temperatures. Furthermore, the presence of the terminal fluorophenyl group enables a subsequent second annulation, yielding a new series of extended polyaromatic mesomorphic compounds, i.e., 1,1',3,3',4,4'-hexafluoro-6,6',7,7',10,10',11,11'-octaalkoxy-2,2'-bitriphenylene (G nm) which were found to display a Col_rec mesophase. The specific nucleophilic substitution patterns of the F n derivatives and the antiparallel stacking mode into columnar structures stabilized by arene-perfluoroarene intermolecular interactions were confirmed by the single-crystal structure of the alkoxy-free side chain analog, i.e., 1,2,4-trifluoro-3-(perfluorophenyl)triphenylene (F). UV-vis absorption and fluorescence emission spectroscopies reveal green photoluminescence with fluorescence quantum yields of up to 33% for the F n derivatives. The J-aggregation for the inner fluorine-substituted dimers G nm is energetically and stereoelectronically more favorable and G66 exhibits thin-film fluorescence with a large red-shift of the emission peak.

The C-H arylation of 2-quinolinecarboxyamide bearing a C-Br bond at the N-aryl moiety is carried out with a palladium catalyst. The reaction proceeds at the C-H bond on the pyridine ring adjacent to the amide group in the presence of 10 mol % Pd(OAc)₂ at 110 °C to afford the cyclized product in 42% yield. The yield is improved to 94% when the reaction is performed with PPh₃ as a ligand of palladium. The reaction is examined with amides derived from unsubstituted picoline, 6-methylpicoline, and 2,6-pyridinedicarboxylic acid in a similar manner to afford the cyclized products in 70%, 77%, and 87% yield, respectively. The related reaction is also carried out with amides of non-pyridine derivatives terephthal- and benzamides to afford multiply fused heterocyclic compounds in 81% and 89% yields, respectively.

Asymmetric cycloaddition is a straightforward strategy which enables the synthesis of structurally distinct cyclic derivatives which are difficult to access by other methodologies, using an efficient and atom-economical path from simple precursors. In recent years several asymmetric catalytic cyclization strategies have been accomplished for the construction of N-heterocycles using various catalytic systems such as chiral metal catalysts, chiral Lewis acids or chiral organocatalysts. This review presents an overview of the recent advances in enantioselective cyclization reactions of 1-azadienes catalyzed by non-covalent organocatalysts.

The marine sponge Suberea ianthelliformis was investigated for new chemistry after the recent discovery that polyamines ianthelliformisamines A-C (1-3) - originally sourced from this Australian sponge - act as Pseudomonas aeruginosa biofilm inhibitors and antibiotic enhancers. Large-scale extraction and isolation studies resulted in the discovery of four new and minor natural products, ianthelliformisamines D-G (4-7) and the known steroid, aplysterol (8). Compounds 4-7 were fully characterised following 1D/2D NMR, MS and UV data analyses. All compounds were assessed for their inhibition on planktonic growth of P. aeruginosa PAO1 in addition to their ability to inhibit the formation of biofilms. None of the tested natural products inhibited planktonic growth or biofilm formation of PAO1 when screened at 50 µM. Ianthelliformisamine D (4) contains a rare N-(3-aminopropyl)-2-pyrrolidone moiety only found in <30 natural products. Owing to the novelty of compound 4, we undertook the first total synthesis of this natural product, which was achieved in three steps.

A new psammaplysin derivative, ceratinadin G (1), was obtained from the Okinawan marine sponge Pseudoceratina sp., and the gross structure was clarified through spectroscopic and spectrometric analyses. The absolute configuration of compound 1 was established by comparing its NMR and ECD data with those of the known psammaplysin derivative, psammaplysin F (2). Ceratinadin G (1) is a rare nitrile containing a cyano group as aminoacetonitrile, and is the first psammaplysin derivative possessing a cyano group. In vitro assays indicated that compound 1 displayed moderate cytotoxicity against L1210 murine leukemia cells and KB epidermoid carcinoma cells.