Synthesis of two nitrogen-containing polyaromatic compounds through gold catalysis/DBU-promoted cyclizations.

This work reports an efficient synthesis of novel benzo[7,8]indolizino[2,3,4,5-ija]quinazoline derivatives between 2-(2-ethynylaryl)acetonitriles 1 and anthranils 2. The synthetic approach involves the initial formation of 7-formylindole intermediates that can be implemented by DBU to activate a novel indole-nitrile-aldehyde cyclization.

Reactions of 1,3-Diphenyl Cyclopentadiene with α-Aryldiazo Ketones to Enable C-H Insertions versus [4 + 2]-Cycloadditions via Au Catalyst and P(C6F5)3 Additive, Respectively.

Two distinct reaction chemoselectivities were reported for the reactions of α-aryldiazo ketone with 1,3-diphenylcyclopentadiene using gold catalyst and phosphine additives, respectively. In the presence of gold catalyst, α-aryldiazo ketone forms gold carbenes initially that are trapped with this 1,3-disubstituted cyclopentadiene to afford C-H insertion products. In the presence of P(C6F5)3 additive, α-aryldiazo ketone forms diarylketenes initially at elevated temperature, which are further stabilized by P(C6F5)3 to secure their entity before proceeding to unprecedented [4C + 2C] cycloadditions.

Stereo- and regiocontrol in intermolecular [2+2] cycloadditions between diarylketenes and allenamides to access substituted α-methylenecyclobutanones.

The development of intermolecular [2+2] cycloadditions between allenamides and diarylketenes is described. α-Aryldiazo arylketones are employed as ketene precursors that react smoothly with allenamides in the presence of a P(C6F5)3 promoter. High diastereoselectivity (dr > 20 : 1) with endo-regioselectivity can be achieved when two aryl groups of ketenes have opposite electronic properties. The role of P(C6F5)3 is to increase the reaction yields, but also enhancing stereoselectivity.

Novel hexameric tin carboxylate clusters as efficient negative-tone EUV photoresists: high resolution with well-defined patterns under low energy doses.

Synthesis of two novel tin carboxylate clusters (RSn)6(R'CO2)8O4Cl2 is described, and their structures have been characterized by X-ray diffraction. These clusters have irregular ladder geometry to form very smooth films with small surface roughness (RMS <0.7 nm) over a large domain. EUV lithography can be used to resolve half pitches (HPs) in the order of 15-16 nm with line width roughness (LWR = 4.5-6.0 nm) using small doses (20-90 mJ cm-2). Cluster 1 (R = n-butyl; R'CO2 = 2-methyl-3-butenoate) contains only a radical precursor and cluster 2 (R = vinyl, R'CO2 = 2-methylbutyrate) bears both a radical precursor and an acceptor; the latter is much better than the former in EUV and e-beam photosensitivity. For these clusters, the mechanisms of EUV irradiation have been elucidated with high resolution X-ray photoelectron spectroscopy (HRXPS) and reflective Fourier-transform infrared spectroscopy (FTIR). At low EUV doses, two clusters undergo a Sn-Cl bond cleavage together with a typical decarboxylation to generate carbon radicals. The n-butyl groups of cluster 1 are prone to cleavage whereas the vinyl-Sn bonds of species 2 are inert toward EUV irradiation; participation of radical polymerization is evident for the latter.

Gold-Catalyzed Addition of ß-Oxo Enols at Tethered Alkynes via a Non-Conia-ene Pathway: Observation of a Formal 1,3-Hydroxymethylidene Migration.

With the relay process of Ag(I)/Au(I) catalysts, a one-pot synthesis of skeletally rearranged (1-hydroxymethylidene)indene derivatives from 2-alkynylbenzaldehydes and α-diazo esters is described. This cascade sequence involves Au(I)-catalyzed 5-endo-dig attack of highly enolizable aldehydes at the tethered alkynes, leading to carbocyclizations with a formal 1,3-hydroxymethylidene transfer. On the basis of density functional theory calculations, the mechanism likely involves formation of cyclopropylgold carbenes, followed by an appealing 1,2-cyclopropane migration.

Catalyst-free diazo cross-coupling to access useful 3(2H)-furanone derivatives.

Catalyst-free synthesis of 3(2H)-furanone derivatives has been achieved from metal-free cross-coupling of α-diazo ester and α-aryldiazo ketones. This reaction sequence comprises a prior Wolff rearrangement of α-aryldiazo ketones to 2-arylketenes, which are trapped in situ with α-diazo esters to form cyclopropanones before undergoing oxa-Nazarov cyclization.

Nitrosoarenes Implement Cascade Cyclization of 1-Allenyl-2-alkynylbenzenes through Diradical Mechanism.

This work reports cascade cyclization between 1-allenyl-2-alkynylbenzenes and nitrosoarenes. When these two components reacted alone under N2, N,O-functionalized indane-fused isoxazolidines 3 were obtained selectively. DFT calculations verify that this reaction sequence involves unprecedented nitrone/alkyne cycloadditions, followed by diradical rearrangement.

Reactions of thioalkynes with diarylketenes via [3+2]-annulation versus benzannulation using Au and P(C6F5)3 catalysts.

Two catalytic annulations of non-symmetric diarylketenes with thioalkynes are described using gold and phosphine catalysts respectively. We employed α-aryldiazo ketones to generate gold-π-ketenes, ultimately yielding azulen-1-one derivatives. With the same reactants, we utilized P(C6F5)3 to increase the yields of 1-naphthols, notably with a complete regioselectivity.

Gold-Catalyzed Rearrangement of α-Carbonyl Cyclopropanes to Form 3-(Cyclopenta-1,3-dien-1-ylmethyl)oxindoles via a Postulated 1,5-Enolate Shift.

Gold-catalyzed stereoselective synthesis of spirocyclopropyl oxindoles from diazooxindoles and 1,2,4-substituted dienes is described. The aim of this work is to report a novel rearrangement of these spirocyclopropyl oxindoles with a gold catalyst to yield 3-(cyclopenta-1,3-dien-1-ylmethyl)oxindoles. Our experimental data exclude a reversible process in the gold-catalyzed cyclopropanation. With DFT calculations, we postulate a rearrangement mechanism involving the formation of complex pairs of gold enolates and 1-methylen-2,3,4-cyclopentadienyl cations, leading to a 1,5-enolate shift.

Gold(I)-Catalyzed [4 + 2] Annulation between Arylynes and C,N-Diaryl Nitrones for Chemoselective Synthesis of Quinoline Scaffolds via Gold Acetylide Intermediates.

Gold-catalyzed synthesis of quinoline derivatives via [4 + 2] annulation between terminal arylynes and nitrones is described. Our mechanistic analysis supports the participation of alkynylgold intermediates, instead of a typical gold-carbene species in recently reported gold catalysis. These nucleophilic alkynylgold species react with nitrones via Povarov-type reactions. Cheap, readily available materials and a broad substrate scope manifest the advantage of this method.

Gold-Catalyzed Bicyclic Annulations of N-(o-Alkynylphenyl)imines with α-Diazo Esters to Form 5,6-Dihydroindolo[2,1-a]isoquinolines.

One-pot synthesis of 5,6-dihydroindolo[2,1-a]isoquinolines from gold-catalyzed annulations between N-(o-alkynylphenyl)imines and α-diazo esters is described. This cascade reaction involves an initial attack of the diazo ester at the imine to form cis-aziridine, followed by stereoselective [3 + 3]-annulations with the tethered arylalkyne. We have employed this new catalysis to prepare one bioactive 5,6-dihydroindolo[2,1-a]isoquinoline molecule.

WSe2/WS2 Heterobilayer Nonvolatile Memory Device with Boosted Charge Retention.

A two-dimensional (2D) nonvolatile memory device architecture to improve the long-term charge retention with the minimum charge loss without compromising storage capacity and the extinction ratio for practical applications has been an imminent demand. To address the current issue, we adopted a novel type-II band-aligned heterobilayer channel comprising vertically stacked monolayer WSe2 nanodots on monolayer WS2. The band offset modulation leads to electron doping from WSe2 nanodots into the WS2 channel without any external driving electric field. As a result, the tested device outperformed with a memory window as high as 34 V and a negligible charge loss of 7% in a retention period of 10 years while maintaining a high extinction ratio of 106. The doping technique presented in this work provides a feasible route to modulate the electrical properties of 2D channel materials without hampering charge transport, paving the way for high-performance 2D memory devices.

Dynamic Kinetic Resolution in Gold-Catalyzed (4 + 2)-Annulations between Alkynyl Benzaldehydes and Allenamides to Yield Enantioenriched All-Carbon Diarylalkylmethane Derivatives.

This work reports the synthesis of diarylmethane derivatives via gold-catalyzed (4 + 2)-annulations between alkynyl benzaldehydes and allenamides, followed by an aza-Claisen rearrangement. Deuterium labeling and crossover experiments have been performed to confirm this proposed mechanism. With racemic 3-substituted allenamides in a substrate ratio (1:1), we employ chiral gold catalysts to achieve a dynamic kinetic resolution to obtain enantioenriched diarylalkylmethane derivatives with high e.r. levels (up to 93:7).

Development of a [2 + 2]-Nitroso/Alkene Cycloaddition Using Sodium Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate Catalyst: Controlled Chemoselectivity of Two Equilibrating Isomeric Intermediates.

Sodium tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (NaBArF) catalyzes the [2 + 2] cycloaddition of 1,4-disubstituted cyclopenta-1,3-dien-2-yl esters with nitrsobenzene in toluene, affording two isolable regioisomers of 6-oxa-7-azabicyclo[3.2.0] heptanes, which thermally rearrange into the same 4-aminocyclopent-1-en-3-ones. In the case of 4-substituted cyclopenta-1,3-dien-2-yl esters, their initial [2 + 2] cycloaddition intermediates undergo a rapid ring expansion to afford six-membered piperidone derivatives efficiently.

Gold-Catalyzed Synthesis of Diaza-hexatrienes Via Diazo Attack at Vinylgold Carbenes: An Easy Access to 1H-Pyrazolo[4,3-b]pyridine-5-ones.

This work reports a gold-catalyzed stereoselective synthesis of highly substituted E-configured 2,3-diaza-1,3,5-hexatrienes using α-diazo nitriles and cyclopropene derivatives; such products arise from an atypical diazo attack of α-aryldiazo nitriles at vinylgold carbenes. For these 2,3-diaza-1,3,5-hexatrienes, we develop a novel anionic cyclization of derivatives of one family to form 1H-pyrazolo[4,3-b]pyridine-5-ones.

Gold Catalysts Can Generate Nitrone Intermediates from a Nitrosoarene/Alkene Mixture, Enabling Two Distinct Catalytic Reactions: A Nitroso-Activated Cycloheptatriene/Benzylidene Rearrangement.

Gold-catalyzed reactions of cycloheptatrienes with nitrosoarenes yield nitrone derivatives efficiently. This reaction sequence enables us to develop gold-catalyzed aerobic oxidations of cycloheptatrienes to afford benzaldehyde derivatives using CuCl and nitrosoarenes as co-catalysts (10-30 mol %). Our density functional theory calculations support a novel nitroso-activated rearrangement, tropylium → benzylidene. With the same nitrosoarenes, we developed their gold-catalyzed [2 + 2 + 1]-annulations between nitrosobenzene and two enol ethers to yield 5-alkoxyisoxazolidines using 1,4-cyclohexadienes as hydrogen donors.

Gold(I)-Catalyzed Oxidative 1,4-Additions of 3-En-1-ynamide with Nitrones via Carbon- versus Nitrogen-Addition Chemoselectivity.

This work reports gold-catalyzed 1,4-oxofunctionalizations of 3-en-1-ynamides with nitrones, yielding two distinct E-configured products. We obtained 1,4-oxoarylation products from 3-en-1-ynamides bearing C(4)-electron-donating substituents and 1,4-oxoamination products from those analogues bearing C(4)-aryl substituents. We propose that if vinylgold carbenes are stable, imines undergo a para-arylation on these gold carbenes. If vinylgold carbenes are highly electron-deficient, this N-attack is irreversible to enable 1,4-oxoaminations.