Organic chemistry frontiers : an international journal of organic chemistry最新文献

β-Lactones are common substructures in bioactive molecules. Herein, we developed an enantioselective N-heterocyclic carbene (NHC)-catalyzed rearrangement of enol ε-lactones for the construction of bicyclic β-lactones. The reaction works well for both exo- and endo-enol ε-lactones, giving the corresponding bicyclic β-lactones with two or three contiguous stereocenters, respectively. The reaction features readily available starting materials, 100% atom economy, mild conditions, high diastereo- and enantioselectivity.

A palladium catalyzed intramolecular C(sp²)–H amination using a readily available aluminum nitrate (Al(NO₃)₃·9H₂O) as the oxidant is reported. The C–H amination is promoted by in situ nitration of the quinoline directing group (DG). The oxindole products can be efficiently converted into novel polycyclic compounds (up to 7 fused rings) via a sequential reduction/cyclization involving the DG. Mechanistic studies indicate that nitration of the quinoline DG favors the following activation of γ-aryl C(sp²)–H bonds over β-methyl C(sp³)–H bonds.

A photoredox catalysed 1,3-oxylallylation of aryl cyclopropanes was accomplished by reaction with carboxylic acids and allyl sulfones. The redox-neutral reaction proceeded in a highly regioselective manner under mild conditions with good functional group compatibility. Simple operation and successful application to the late-stage functionalization of several natural product and pharmaceutical molecule related carboxylic acids add extra merits to the current protocol.

High efficiency and high color purity are two key factors for achieving non-doped deep-blue organic light-emitting diodes (OLEDs). Herein, a novel emitter 3,6-di-tert-butyl-9-(4′-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole (DTPCZTZ) with a weak donor–acceptor structure containing carbazole as the donor and triazole as the acceptor was designed and synthesized. Photophysics and theoretical calculation show that it has the hybridized local and charge-transfer (HLCT) state. A subtle introduction of tert-butyl on carbazole combined with twisted 3,4,5-triphenyl-4H-1,2,4-triazole endows the molecule with a highly twisted molecular conformation, and it successfully achieves a deep-blue emission. And the non-doped device based on DTPCZTZ showed a electroluminescence (EL) peak at 424 nm, the Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.06), and the maximum external quantum efficiency (EQE_max) up to 7.6%, and is one of the best non-doped OLEDs with pure organic deep-blue HLCT molecules. Importantly, the application potential of DTPCZTZ in phosphorescent OLEDs (PhOLEDs) is also evaluated based on Ir(PPy)₂(acac) and Ir(MDQ)₂(acac) as the dopants and DTPCZTZ as the host, and high-efficiency green and red PhOLEDs with an EQE_max, maximum power efficiency (PE_max), maximum current efficiency (CE_max), and maximum luminance (L_max) of up to 20.1%, 81.5 lm W⁻¹, 72.6 cd A⁻¹, and 29 595 cd m⁻² and 15.3%, 22.1 lm W⁻¹, 21.1 cd A⁻¹, and 10 526 cd m⁻², respectively, were successfully realized. These results provide a valuable strategy for the design of highly efficient deep-blue emitters and using them as host materials, having significant potential for practical applications.

A palladium-catalyzed asymmetric (4 + 3) cycloaddition of N-2,2,2-trifluoroethylisatin ketimines with 2-methylidenetrimethylene carbonate was reported to enantioselectively afford trifluoromethylated spirooxindoles in moderate yields and good to excellent ee values. Experimentally, the reaction proceeded smoothly in the absence of a Brønsted base in a one-pot manner, which paved a way for efficient and cost-effective construction of optically pure trifluoromethylated medium-sized rings.

The mechanism and stereoselectivity of the Ni(ii)-catalyzed [3 + 3] annulation between donor–acceptor cyclopropanes (DACs) and diaziridines were studied by DFT calculations. The obtained results show that the entire reaction comprises three main steps: (1) nucleophilic attack of diaziridines on DACs to form a quaternary ammonium intermediate; (2) cleavage of the unstable C–N bond in the quaternary ammonium intermediate to generate the key intermediate; (3) cyclization of the key intermediate involving two carbon atoms with opposite charges to obtain products with different configurations via distinct six-membered ring transition states. Based on the calculation results, the reaction between DACs of R-configuration and diaziridines with five-membered ring substituents leads to a predominant E-configuration product. However, Z-configuration products are the major outcome of the reactions involving S-configuration DACs. When R-configuration DACs react with diaziridines containing six-membered rings, the key intermediates of Z-configuration are more stable, thus resulting in the main products with Z-configuration. Furthermore, the distortion/interaction analysis revealed that the configuration of the final product is dominated by the distortion energy and is closely related to that of the key intermediate. This theoretical study might provide new perspectives toward predicting the reaction pathways and rationalizing selectivity features in related types of annulation reactions.

A facile and efficient synthesis of bicyclic 1,3-oxazin-4-ones, 2,3,6,7-tetrahydrocyclopenta[e]-1,3-oxazin-4-ones and 2,3,5,6,7,8-hexahydro-4H-benzo[e]-1,3-oxazin-4-ones, has been achieved via an Ir-catalyzed one-pot reaction of secondary amides with adipoyl chloride and pimeloyl chloride, respectively. This method features good yields, broad substrate scope, mild reaction conditions, and scalability. This reaction also shows good compatibility with acetyl chloride and phenylacetyl chloride to access monocyclic 1,3-oxazin-4-ones.

The base-catalyzed addition of alkynylsilanes to ketone derivatives enables the formation of various silyl-protected propargylic alcohols. Commercially available and inexpensive potassium bis(trimethylsilyl)amide (KHMDS) serves as an efficient transition metal-free catalyst and permits the functionalization of a variety of derivatives, including pharmaceuticals and biorelevant compounds. Overall, the presented system complements classical routes to protected tertiary propargylic alcohols that mainly rely on stoichiometric processes or fluoride-mediated reactions.

Chiral organophosphoric acids have made a huge contribution in the context of asymmetric organocatalysis. Surprisingly, the application of chiral organophosphates as ligands in asymmetric metal-catalysis is less well-studied. However, based on the number of different readily available chiral phosphates (e.g. biphenyl phosphates, binaphthyl phosphates, spirocyclic phosphates or vaulted biphenanthrol phosphates) and the large number of available metal sources, this area of research offers many exciting possibilities. In this Minireview, the most recent examples of chiral metal-phosphate catalysis are discussed, including main-group catalysis using Li-, Mg-, Ca-, In- or Bi-phosphates, transition-metal catalysis using Ti-, Mn-, Rh-, Pd-, Ag- and Au-phosphates and catalysis by rare-earth metals based on Yb-phosphates.

With N-methyl-4-aminoindole as the 1,4-bisnucleophile, the regio- and enantioselective Friedel–Crafts alkylation/N-hemiacetalization and dehydration sequence with β,γ-unsaturated α-ketoesters was reported using 5 mol% Ni(ii)-PyBPI complex, affording diverse chiral 7-membered-ring-bridged 3,4-fused tricyclic indoles in good results (up to 91% yield and 97% ee). The by-products were 6-membered-ring-bridged 4,5-fused tricyclic indoles.