Lewis-Acid-Mediated Intramolecular Cyclization of 4-Aryl-5-allyl-1,2,3-triazoles to Substituted Cyclopentene Derivatives

4-Aryl-5-allyl-N-fluoroalkyl-1,2,3-triazoles available by a three-component reaction of fluoroalkyl azides, copper acetylides, and allyl halides underwent aluminum halide-mediated transformation to N-(4-halo-2-aryl-cyclopentenyl) imidoyl halides by cyclization of vinyl cation intermediates, followed by halide capture. Utilization of the cyclic products was demonstrated by the synthesis of N-alkenyl amides, amidines, isoquinolines, and tetrazoles or by the subsequent modification of the cyclopentene ring.

Gold(I)-Catalyzed Benzylic C(sp3 )-H Functionalizations: Divergent Synthesis of Indole[a]- and [b]-Fused Polycycles

Phenyl azides substituted by an (alkylphenyl)ethynyl group facilitate benzylic sp³ (C-H) functionalization in the presence of a JohnPhosAu catalyst, resulting in indole-fused tetra- and pentacycles via divergent N- or C-cyclization. The chemoselectivity is influenced depending on the counter-anion, the electron density of the α-imino gold(I) carbene, and the alkyl groups stabilizing the benzylic carbocation originating from a 1,5-hydride shift. An isotopic labeling experiment demonstrates the involvement of an indolylgold(I) species resulting from a tautomerization that is much faster than the deauration. The formation of a benzylic sp³ (C-H) functionalization leading to an indole-fused seven-membered ring is also demonstrated.

Construction of Tricyclic Nitrogen Heterocycles by a Gold(I)-Catalyzed Cascade Cyclization of Allenynes and Application to Polycyclic π-Electron Systems

A novel approach to the direct construction of tricyclic nitrogen heterocycles based on gold-catalyzed cascade cyclization of aminoallenynes is described. The expected biscyclization reaction of hydroxyisobutyryl-protected aminoallenynes was efficiently promoted by a catalytic amount of BrettPhosAuNTf₂ in the presence of iPrOH to produce 1,2-dihydrobenzo[cd]indole derivatives in good yields. When the reaction was combined with Friedel-Crafts acylation or palladium-catalyzed N-arylation, the resulting tricyclic products were efficiently converted into nitrogen-containing polycyclic aromatic compounds (N-PACs) with highly conjugated π-electron systems. A newly obtained hexacyclic indolium salt showed characteristic concentration-dependent absorption and emission properties.

Impact of Boron Acceptors on the TADF Properties of Ortho-Donor-Appended Triarylboron Emitters

We report the impact of boron acceptors on the thermally activated delayed fluorescence (TADF) properties of ortho-donor-appended triarylboron compounds. Different boryl acceptor moieties, such as 9-boraanthryl (1), 10H-phenoxaboryl (2), and dimesitylboryl (BMes₂, 3) groups have been introduced into an ortho donor (D)–acceptor (A) backbone structure containing a 9,9-diphenylacridine (DPAC) donor. X-ray crystal diffraction and NMR spectroscopy evidence the presence of steric congestion around the boron atom along with a highly twisted D–A structure. A short contact of 2.906 Å between the N and B atoms, which is indicative of an N → B nonbonding electronic interaction, is observed in the crystal structure of 2. All compounds are highly emissive (PLQYs = 90–99%) and display strong TADF properties in both solution and solid state. The fluorescence bands of cyclic boryl-containing 1 and 2 are substantially blue-shifted compared to that of BMes₂-containing 3. In particular, the PL emission bandwidths of 1 and 2 are narrower than that of 3. High-efficiency TADF-OLEDs are realized using 1–3 as emitters. Among them, the devices based on the cyclic boryl emitters exhibit pure blue electroluminescence (EL) and narrower EL bands than the device with 3. Furthermore, the device fabricated with emitter 1 achieves a high external quantum efficiency of 25.8%.