Search

Precisely introducing topological defects is an important strategy in nanographene crystal engineering because defects can tune π‐electronic structures and control molecular assemblies. The synergistic control of the synthesis and assembly of nanographenes by embedding the topological defects to afford two‐dimensional (2D) crystals on surfaces is still a great challenge. By in‐situ embedding ladder bipyrazinylene (LBPy) into acene, the narrowest nanographene with zigzag edges, we have achieved the precise preparation of 2D nonbenzenoid heteroacene crystals on Au(111). Through intramolecular electrocyclization of o‐diisocyanides and Au adatom‐directed [2+2] cycloaddition, the nonbenzenoid heteroacene products are produced with high chemoselectivity, and lead to the molecular 2D assembly via LBPy‐derived interlocking hydrogen bonds. Using bond‐resolved scanning tunneling microscopy, we determined the atomic structures of the nonbenzenoid heteroacene product and diverse organometallic intermediates. The tunneling spectroscopy measurements revealed the electronic structure of the nonbenzenoid heteroacene, which is supported by density functional theory (DFT) calculations. The observed distinct organometallic intermediates during progression annealing combined with DFT calculations demonstrated that LBPy formation proceeds via electrocyclization of o‐diisocyanides, trapping of heteroarynes by Au adatoms, and stepwise elimination of Au adatoms. [ABSTRACT FROM AUTHOR]

[3]Radialenes are the smallest carbocyclic structures with unusual topologies and cross‐conjugated π‐electronic structures. Here, we report a novel [1+1+1] cycloaddition reaction for the synthesis of aza[3]radialenes on the Ag(111) surface, where the steric hindrance of the chlorine substituents guides the selective and orientational assembling of the isocyanide precursors. By combining scanning tunneling microscopy, non‐contact atomic force microscopy, and time‐of‐flight secondary ion mass spectrometry, we determined the atomic structure of the produced aza[3]radialenes. Furthermore, two reaction pathways including synergistic and stepwise are proposed based on density functional theory calculations, which reveal the role of the chlorine substituents in the activation of the isocyano groups via electrostatic interaction. [ABSTRACT FROM AUTHOR]

Although post‐functionalization is extensively used to introduce diverse functional groups into supramolecular polymers (SPs) in solution, post‐functionalization of SPs on surfaces still remains unexplored. Here we achieved the on‐surface post‐functionalization of two SPs derived from 5,10,15‐tri‐(4‐pyridyl)‐20‐bromophenyl porphyrin (Br‐TPyP) via cross‐coupling reactions on Au(111). The ladder‐shaped, Cu‐coordinated SPs preformed from Br‐TPyP were functionalized through Heck reaction with 4‐vinyl‐1,1′‐biphenyl. In the absence of Cu, Br‐TPyP formed chiral SPs as two enantiomers via self‐assembly, which were functionalized via divergent cross‐coupling reaction with 4‐isocyano‐1,1′‐biphenyl (ICBP). Surprisingly, this reaction was discovered as an enantioselective on‐surface reaction induced by the chirality of SPs. Mechanistic analysis and DFT calculations indicated that after debromination of Br‐TPyP and the first addition of ICBP, only one attack direction of ICBP to the chiral SP intermediate is permissive in the second addition step due to the steric hindrance, which guaranteed the high enantioselectivity of the reaction. [ABSTRACT FROM AUTHOR]

A transition-metal-free double addition/double rearrangement domino reaction affording CF3-substituted pyrimidines was developed, which enables the one-pot construction of five new bonds, namely three C–C bonds and two C–N bonds. The keys to achieve this highly efficient reaction include the delicate design of the bis-nucleophiles in situ generated from the dimerization of alkyl nitriles and the use of trifluoroacetimidoyl nitriles containing C＝N, C≡N, and CF3 groups as the reactant. The mechanistic studies by the experiments and DFT calculations reveal that the transformation involves two addition and two unprecedented rearrangement processes. [ABSTRACT FROM AUTHOR]

A highly efficient palladium-catalyzed cascade annulation of 2-vinylbenzaldehydes with indoles has been achieved to afford 6-(3-indolyl)benzo[b]carbazoles under mild conditions in good yield and with excellent regioselectivity. Mechanistic investigations reveal that the reaction proceeds via double addition of indoles, unexpected intramolecular 1,4-aryl and 1,2-hydrogen migrations, and oxidative aromatization. [ABSTRACT FROM AUTHOR]

A novel cascade reaction of internal alkynols with 1-(2-aminophenyl)prop-2-ynols has been developed to form a new N,O-containing fused 5,5,6-tricyclic skeleton. Mechanistic studies indicate that this reaction proceeds via alkynol cycloisomerization, intermolecular substitution with 1-(2-aminophenyl)prop-2-ynols, and intermolecular addition with alkynols and consequent cyclizations. In this way, two C–C bonds, one C–O bond and one C–N bond form to give a tricyclic skeleton in a single reaction. [ABSTRACT FROM AUTHOR]

We employed three metal-coordination structures as templates to control the Sonogashira cross-coupling reactions on a Au(111) surface catalyzed by loaded Pd. We used scanning tunnelling microscopy to resolve the products formed at the successive reaction steps and identified three vital characteristics for an efficient template: high accessibility of reaction sites, structural rigidity and thermal stability. [ABSTRACT FROM AUTHOR]

The efficiency of Ullmann reaction of aryl chlorides on an Au(111) surface has been substantially increased by using dosed Cu as a catalyst. The different reactivity of aryl bromides and aryl chlorides has been exploited to design a programmed, on-surface synthesis to form 2D covalent organic frameworks. [ABSTRACT FROM AUTHOR]

A convenient palladium-catalyzed tandem reaction of aryl iodides and salicyl N-tosylhydrazones has been achieved to afford a series of compounds containing the novel spiro[benzofuran-3,2′-chromene] scaffold in moderate to good yields. This efficient catalytic reaction, which tolerates various functional groups, combines alkyne-based 5- exo- dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization, generating three new bonds in one reaction. [ABSTRACT FROM AUTHOR]

Two tunable cascade reactions of alkynols and alkynes have been developed by combining Sc(OTf)3 and rhodium catalysis. In the absence of H2O, an endo-cycloisomerization/C–H activation cascade reaction provided 2,3-dihydronaphtho[1,2-b]furans in good to high yields. In the presence of H2O, the product of alkynol hydration underwent an addition/C–H activation cascade reaction with an alkyne, which led to the formation of 4,5-dihydro-3H-spiro[furan-2,1′-isochromene] derivatives in good yields under mild reaction conditions. Mechanistic studies of the cascade reactions indicated that the rate-determining step involves C–H bond cleavage and that the hydration of the alkynol plays a key role in switching between the two reaction pathways. [ABSTRACT FROM AUTHOR]

Cross-coupling is of great importance in organic synthesis. Here it is demonstrated that cross-coupling of aryl-bromide and porphyrin-bromide takes place on a Au(111) surface in vacuo. The products are oligomers consisting of porphyrin moieties linked by p-phenylene at porphyrin's meso-positions. The ratio of the cross-coupled versus homocoupled bonds can be regulated by the reactant concentrations. Kinetic Monte Carlo simulations were applied to determine the activation barrier. It is expected that this reaction can be employed in other aryl-bromide precursors for designing alternating co-polymers incorporating porphyrin and other functional moieties. [ABSTRACT FROM AUTHOR]

A ruthenium complex with a tetradentate nitrogen-phosphorus mixed ligand is shown to be an efficient catalyst for domino addition/ exo-cycloisomerization of propargylic alcohols and tosyl isocyanate. In the presence of 2-5 mol% ruthenium complex, a range of terminal propargylic alcohols were reacted with tosyl isocyanate to furnish the corresponding oxazolidinone product exclusively in moderate to excellent yields. Mechanistic studies suggest that propargylic alcohol and tosyl isocyanate undergo addition firstly to generate propargylic carbamate, which is then activated by the ruthenium complex to form an η2-alkyne complex, rather than the ruthenium vinylidene intermediate, to afford the final oxazolidinone product. [ABSTRACT FROM AUTHOR]

Rhodium-catalyzedaddition–cyclization of hydrazines withalkynes has been achieved to afford highly substituted pyrazoles undermild conditions. The cascade reaction involves two transformations:addition of the C–N bond of hydrazines to alkynes via unexpectedC–N bond cleavage and intramolecular dehydration cyclization. [ABSTRACT FROM AUTHOR]

Intermolecular benzylic methylene functionalization of exo-cyclic enol ethers has been achieved using imines as reagents and potassium tert-butoxide as the catalyst. Depending on the solvent used, the reaction proceeds by two pathways. In THF, an addition/elimination reaction of exo-cyclic enol ethers with imines provides dihydroisobenzofuran derivatives in good yield. In DMSO, an addition/ring-opening/cyclization cascade reaction occurs with unexpected cleavage of C–O and C–C bonds, affording isoquinolin-1(2H)-one products in high yield under ambient reaction conditions. [ABSTRACT FROM AUTHOR]

A tetradentate nitrogen-phosphorus ligand is used for the ruthenium-catalyzed title reaction with high exo-selectivity. [ABSTRACT FROM AUTHOR]

The rhodium-catalyzed oxidative annulation of aromatic hydrazines with various alkynes affords aminoindol derivatives. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Selective Cyclization of Alkynols and Alkynylamines Catalyzed by Potassium tert-Butoxide" by D.Y. Li and others, published in the periodical "Tetrahedron" in 2014.

The article presents chemical equations related to the solvent-switched benzylic methylene functionalization by studying ring-opening, addition, cyclization and cleavage of carbon (C)-oxygen (O) and C-C bonds published in the "Organic Letters" in 2013.