Beilstein Journal of Organic Chemistry最新文献

Solvent-dependent transformations of polysubstituted 2-acetyl-2,5-dihydrothiophenes to the corresponding 2-hydroxy- or deacetylated derivatives are described. The treatment of a methanolic solution of the dihydrothiophene substrates with sodium methoxide afforded the deacylated products. Conversely, the treatment with sodium ethoxide in an oxygen saturated ethanolic solution produced 2-hydroxy substituted 2,5-dihydrothiophenes.

In the course of screening vancomycin-resistant enterococci (VRE), two new meroterpenoids, streptoquinolines A (1) and B (2), were isolated from a culture of terrestrial Streptomyces sp. TMPU-A0679. The structures of 1 and 2 were elucidated based on spectroscopic analyses, including NMR and MS, and were found to consist of a drimane-type sesquiterpene fused with a highly substituted quinoline moiety. Further structural comparisons and specific rotation data revealed that 1 and 2 were epimers at C-4'. Compounds 1 and 2 both exhibited selective antibacterial activity against Gram-positive bacteria, including VRE and methicillin-resistant Staphylococcus aureus, with minimum inhibitory concentrations ranging from 6.25 to 12.5 µg/mL. These results expand the structural and biological diversities of drimane-quinoline-type meroterpenoids and highlight their potential as lead compounds for the development of new antibacterial agents targeting drug-resistant Gram-positive pathogens.

25CN-NBOH is a selective serotonin 2A receptor agonist used extensively as a tool compound in preclinical research. Herein, we perform an in-depth characterization of 25CN-NBOH and report key physicochemical properties in the solid state as well as in the solution state, namely stability, ionization, solubility, partition coefficient, and membrane permeability. We show that the hydrochloride salt is a stable and well-defined crystalline compound that is also stable in aqueous solutions at room temperature. Furthermore, we show that an intramolecular hydrogen bond is present in solution, which presumably is a key contributor to the high membrane permeability. Collectively, this physical-chemical profiling of 25CN-NBOH provides guidance to researchers with respect to the physiochemical properties and handling of the compound in various research scenarios.

6,6'-Dibromoindigo is the major component of a historic pigment, famous since ancient times, known as Tyrian purple. In this work, we report a new strategy for the synthesis of 6,6'-dibromoindigo in four steps from p-bromotoluene in 14.5% overall yield. A key improvement in the reported synthesis is the oxidation of the benzylic methyl group of 4-bromo-2-nitrotoluene to 4-bromo-2-nitrobenzaldehyde, which is accomplished by benzylic bromination followed by a Kornblum oxidation. This gentle oxidation avoids the need for chromium trioxide-mediated or nitrone-based methods. While other published syntheses of 6,6'-dibromoindigo have resulted in higher overall yields, our approach offers the advantages of inexpensive starting reagents, operationally simple reactions, and minimal purification of intermediates. Moreover, this work reports the successful sulfonation of 6,6'-dibromoindigo, producing water-soluble derivatives of this historically relevant dye.

A selective and efficient method for the synthesis of sulfinimidate esters via an NBS-promoted oxidative coupling of sulfenamides with alcohols has been developed. This operationally simple, metal-free protocol uses inexpensive and readily available reagents, operates under mild conditions, exhibits a broad substrate scope and high chemoselectivity, and clearly distinguishes itself from classical Mukaiyama-type oxidations. The reaction is readily scalable to gram quantities and is applicable to late-stage functionalization of complex alcohols, including bioactive molecules such as RU58841. Moreover, chiral alcohols such as ʟ-menthol are well tolerated, affording diastereomeric sulfinimidate esters that can undergo stereospecific Grignard substitutions to furnish enantioenriched sulfilimines with up to 93% ee. These results demonstrate the potential of sulfinimidate esters as versatile intermediates for enantioselective S-C bond formation under mild and metal-free conditions.

Various multifunctional enantiomerically pure organocatalysts were synthesized and screened in asymmetric Mannich reaction. The reaction of aromatic imines with malonates in the presence of amino acid-derived catalysts gave Mannich adducts in very high enantiomeric purities (up to 98% ee). It is proposed that a network of hydrogen and halogen bonds with Lewis bases, together with the steric effect of the tert-butyl group of the catalyst, is responsible for the high stereoselectivity of the reaction.

A pair of an axially chiral platinum(II) complex was synthesized via Sonogashira coupling and subsequent coordination of a pincer ligand to a precursor. The complex exhibited a broad absorption band ranging from 250 to 550 nm in the UV-vis spectrum, with TD-DFT calculations indicating mixed ligand-to-ligand charge transfer (LL'CT) and metal-to-ligand charge transfer (MLCT) character. Photoluminescence measurements in CH₂Cl₂ solution revealed dual emission peaks at 427 nm and 596 nm, with a quantum yield of 3%. In PMMA matrix, the emission peaks were blue-shifted to 408 nm and 558 nm, and the quantum yield slightly increased to 4%. CD spectra showed distinct Cotton effects in the MLCT region, and CPL signals were observed only in the PMMA matrices, with a dissymmetry factor |g _lum| = 0.4 × 10^-3. These results demonstrate that axial chirality of the binaphthyl moiety governs the three-dimensional chiral arrangement of two platinum(II) chromophore units, leading to the chiroptical properties in the MLCT region through exciton coupling under restricted molecular motion.

Three indan-2-one-based donor-π-acceptor-π-donor type dyes with symmetric donor groups were synthesized and characterized to study their nonlinear optical (NLO) properties and their potential use in the rapid and selective determination of cyanide. The designed structures feature symmetrical alkylaminophenyl donor groups and a strong electron-withdrawing dicyanovinylene as an acceptor connected through vinyl groups as a π-bridge. These strongly π-conjugated organic dyes can absorb in the NIR region, and they showed sensitivity towards the polarity of solvents with colorimetric and optical changes. Because of the strong donor-acceptor structure, second-order NLO properties were studied by measuring electric field-induced second harmonic (EFISH) values, which showed significant second-order NLO responses. The experimental results were explained using density functional theory (DFT) methods. The dyes also exhibit chemosensor properties, showing selectivity for cyanide via a Michael addition mechanism that causes the disappearance of the ICT band, and a significant color change was observed in both organic and aqueous media. In addition, the interaction mechanism between cyanide and the chemosensor is determined by a ¹H NMR study and explained by DFT calculations.

New highly electrophilic gem- and spiro-activated trichloromethylnitrocyclopropanes were obtained by the Michael-initiated ring closure (MIRC) reaction of 1-bromo-1-nitro-3,3,3-trichloropropene with linear and cyclic CH-acids catalyzed by bases. Conditions for obtaining the target cyclopropanes were optimized. The process is characterized by high diastereoselectivity and allows obtaining cyclopropanes with trans-configuration of -NO₂ and -CCl₃ groups. Monocyclic (based on malonic acid dinitrile, methyl cyanoacetate, ethyl cyanoacetate, benzoylacetonitrile), spirocarbo- (based on 1,3-indanedione) and spiroheterocyclic (based on Meldrum's acid, dimethylbarbituric acid, 3-methyl-1-phenyl-5-pyrazolone) cyclopropane structures were isolated and characterized.

Arenes and heteroarenes are easily available building blocks in organic chemistry, and saturation the aromatic ring facilitates synthetic chemists to efficiently synthesize natural products with complex three-dimensional structures. Recent advances in catalyst and ligand design have enabled unprecedented progress in the catalytic hydrogenation of (hetero)aromatic systems. Quinoline, isoquinoline, pyridine, and related substrates can now be reduced with high efficiency and stereoselectivity, providing efficient access to saturated and partially saturated architectures vital to synthetic chemistry. Furthermore, catalytic asymmetric aromatic hydrogenation has facilitated the asymmetric total synthesis of complex natural products and pharmaceutical agents. This review highlights recent advances in catalytic (hetero)arene hydrogenation, with a focus on its application in natural product synthesis.