Synthesis of Isocoumarins through Three‐Component Couplings of Arynes,Terminal Alkynes,and Carbon Dioxide Catalyzed by an NHC–Copper Complex

A copper‐catalyzed multicomponent coupling reaction between in situ generated ortho‐arynes, terminal alkynes, and carbon dioxide was developed to access isocoumarins in moderate to good yields. The key to this CO₂‐incorporating reaction was the use of a versatile N‐heterocyclic carbene/copper complex that was able to catalyze multiple transformations within the three‐component reaction.     

Hydroboration of Arynes with N‐Heterocyclic Carbene Boranes

Arynes were generated in situ from ortho‐silyl aryl triflates and fluoride ions in the presence of stable N‐heterocyclic carbene boranes (NHC? BH₃). Spontaneous hydroboration ensued to provide stable B‐aryl‐substituted NHC‐boranes (NHC? BH₂Ar). The reaction shows good scope in terms of both the NHC‐borane and aryne components and provides direct access to mono‐ and disubstituted NHC‐boranes. The formation of unusual ortho regioisomers in the hydroboration of arynes with an electron‐withdrawing group supports a hydroboration process with hydride‐transfer character.     

1,2‐Azaborine: The Boron‐Nitrogen Derivative of ortho‐Benzyne

The BN analogue of ortho‐benzyne, 1,2‐azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N₂ and CO₂, thus demonstrating its highly reactive nature. The interaction with N₂ is photochemically reversible. The CO₂ adduct of 1,2‐azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO₂ splitting.     

Synthesis of Distorted 1,8,13-Trisilyl-9-hydroxytriptycenes by Triple Cycloaddition of Ynolates to 3-Silylbenzynes

1,8,13-Trialkyl(aryl)silyl-9-hydroxytriptycenes (trisilyltriptycenes) were synthesized by the triple addition of ynolates and 3-silylbenzynes with high regioselectivity. Benzene rings in the resulting triptycenes were highly distorted where the dihedral angles between the substituents were as high as 35°. The distortion energy induced step-by-step halogenation reactions to yield halogenated triptycenes, including chiral triptycenes. The 1,8,13-trihalogenated triptycenes were then converted to 1,8,13-functionalized triptycenes.     

Synthesis and Absorption Properties of Long Acenoacenes

Acenes, polyaromatic hydrocarbons composed of linearly fused benzene rings have received immense attention due to their performance as semiconductors in organic optoelectronic applications. Their appealing physicochemical properties, such as extended delocalization, high charge carrier mobilities, narrow HOMO-LOMO gaps and partially radical character in the ground state make them very attractive targets for many potential applications. However, the intrinsic synthetic challenges of unsubstituted members such as high reactivity and poor solubility are still limiting factors for their wider exploitation. Herein, we report a simple general synthesis of a new family of angularly fused acenoacenes with improved stability compared to their isoelectronic linear counterparts. The synthesis and comprehensive characterization of pentacenopentacene, pentacenohexacene and hexacenohexacene, with lengths between decacene and dodecacene, are disclosed.     

Synthesis of Enantiopure Benzo Fused Cyclic Sulfoximines Through Stereoselective [3+2] Cycloaddition between N-tert-Butanesulfinyl [(2-Pyridyl)sulfonyl]-difluoromethyl Ketimines and Arynes

The previously developed stereoselective [3+2] cycloaddition between N-tert-butanesulfinyl ketimines and arynes has been extended to the synthesis of enantiopure [(2-pyridyl)sulfonyl]difluoromethylated cyclic sulfoximines. The use of 2-PySO₂CF₂ as the facilitating group offers new opportunities for the elaboration of the [3+2] cycloaddition products by virtue of the diverse relativity of 2-pyridyl sulfones.     

Cyclotrimerization reactions of arynes and strained cycloalkynes

The use of arynes and related species as substrates in metal-catalyzed cycloaddition reactions leads to structurally interesting products. Palladium-catalyzed cyclotrimerization of arynes provides a new method for the synthesis of polycyclic aromatic hydrocarbons. For instance, the chemoselective formal [2 + 2 + 2] cocycloaddition of 2,3-triphenylynes with alkynes affords extended triphenylenes, which are good candidates to behave as liquid crystals. Cotrimerization of benzyne and electron-deficient alkenes selectively affords dihydrophenanthrenes or ortho-olefinated biaryls depending on the catalytic system employed. The use of 2,2'-bis(diphenylphosphino)-1,1'-binophythyl (BINAP)-based palladium(0) catalysts in the cocyclotrimerization of 7-methoxynaphthalyne and dimethyl acetylenedicarboxylate affords an enantiomerically enriched tetrasubstituted pentahelicene, the first example of a metal-catalyzed enantioselective reaction involving arynes. Strained cyclic alkynes can also participate in the palladium-catalyzed cyclotrimerization reactions, which again lead to structurally interesting products.