Aromatic cations from oxidative carbon-hydrogen bond cleavage in bimolecular carbon-carbon bond forming reactions

Chromenes and isochromenes react quickly with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form persistent aromatic oxocarbenium ions through oxidative carbon-hydrogen cleavage. This process is tolerant of electron-donating and electron-withdrawing groups on the benzene ring and additional substitution on the pyran ring. A variety of nucleophiles can be added to these cations to generate a diverse set of structures.     

An approach to mimicking the sesquiterpene cyclase phase by nickel-promoted diene/alkyne cooligomerization

Artificially mimicking the cyclase phase of terpene biosynthesis inspires the invention of new methodologies, since working with carbogenic frameworks containing minimal functionality limits the chemist's toolbox of synthetic strategies. For example, the construction of terpene skeletons from five-carbon building blocks would be an exciting pathway to mimic in the laboratory. Nature oligomerizes, cyclizes, and then oxidizes γ,γ-dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP) to all of the known terpenes. Starting from isoprene, the goal of this work was to mimic Nature's approach for rapidly building molecular complexity. In principle, the controlled oligomerization of isoprene would drastically simplify the synthesis of terpenes used in the medicine, perfumery, flavor, and materials industries. This article delineates our extensive efforts to cooligomerize isoprene or butadiene with alkynes in a controlled fashion by zerovalent nickel catalysis building off the classic studies by Wilke and co-workers.     

Three-dimensional spatiotemporal pulse characterization with an acousto-optic pulse shaper and a Hartmann-Shack wavefront sensor

We demonstrate a simplified arrangement for spatiotemporal ultrashort pulse characterization called Hartmann-Shack assisted, multidimensional, shaper-based technique for electric-field reconstruction. It employs an acousto-optic pulse shaper in combination with a second-order nonlinear crystal and a Hartmann-Shack wavefront sensor. The shaper is used as a tunable bandpass filter, and the wavefronts and intensities of quasimonochromatic spectral slices of the pulse are obtained using the Hartmann-Shack wavefront sensor. The wavefronts and intensities of the spectral slices are related to one another using shaper-assisted frequency-resolved optical gating measurements, performed at particular points in the beam. This enables a three-dimensional reconstruction of the amplitude and phase of the pulse. We present some example pulse measurements and discuss the operating parameters of the device.     

Polydopamine as a Visible-Light Photosensitiser for Photoinitiated Polymerisation

Polydopamine (PDA) is a synthetic model for melanin and has a wide range of opto-electronic properties that underpin its utility in applied and biological settings, from broadband light absorbance to possessing stable free radical species. Here, we show that PDA free radicals are photo-responsive under visible light irradiation, enabling PDA to serve as a photo-redox catalyst. Steady-state and transient electron spin resonance spectroscopy reveals a reversible amplification in semiquinone radical population within PDA under visible light. This photo-response modifies the redox potential of PDA and supports sensitisation of exogenous species via photoinduced electron transfer (PET). We demonstrate the utility of this discovery by employing PDA nanoparticles to photosensitise a common diaryliodonium photoinitiator and initiate free-radical polymerisation (FRP) of vinylic monomers. In situ ¹H nuclear magnetic resonance spectroscopy reveals an interplay between PDA-driven photosensitising and radical quenching during FRP under blue, green, and red light. This work provides crucial insights into the photoactive free radical properties of melanin-like materials and reveals a promising new application for polydopamine as a photosensitiser.     

Preparation of substituted 1,2,3,4-tetrahydroquinoxalines and 2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepines from catalytic CpIr hydrogen transfer N-heterocyclization of anilino alcohols

The [Cp^∗IrCl₂]₂/K₂CO₃ catalyzed hydrogen transfer N-heterocyclization on a series of anilino alcohols has been investigated. The catalyst (20% loading) converts anilino alcohols to 1,2,3,4-tetrahydroquinoxalines and 2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepines in 30-84% isolated yield.     

5‐Aminonaphthalene‐1‐sulfonic acid and its manganese,nickel and cobalt salts

5‐Ammonionaphthalene‐1‐sulfonate monohydrate, C₁₀H₉NO₃S·H₂O, contains layers of zwitterionic molecules with the acidic sulfonic acid H atom transferred to the amine N atom. Within each layer, the charged groups (NH₃⁺ and SO₃⁻) are directed to the surface of the layer and are inverted on adjacent molecules. The naphthalene rings in a given layer are all parallel. The layers are held together by N—H...O and O—H...O hydrogen bonds involving the ammonium, sulfonate and water atoms. The Mn and Ni salts crystallize as fully aquated trihydrates, namely hexaaquamanagnese(II) bis(5‐aminonaphthalene‐1‐sulfonate) trihydrate, [Mn(H₂O)₆](C₁₀H₈NO₃S)₂·3H₂O, (II), and hexaaquanickel(II) bis(5‐aminonaphthalene‐1‐sulfonate) trihydrate, [Ni(H₂O)₆](C₁₀H₈NO₃S)₂·3H₂O, (III), in which layers of hexaaquametal(II) complexes alternate with layers of 5‐aminonaphthalene‐1‐sulfonate anions. The cations reside on twofold rotation axes and display regular octahedral coordination. The additional water molecules are found in the inorganic layer between the complex cations, one on a twofold axis and one in a general position. The anions are packed in a herring‐bone arrangement with the rings of neighboring rows of anions approximately 43° out of parallel. The NH₂ and SO₃⁻ groups line the surface of the layer, where they participate in numerous hydrogen bonds with the water molecules. Whereas the Mn and Ni salts are orthorhombic, the Co salt, hexaaquacobalt(II) bis(5‐aminonaphthalene‐1‐sulfonate) dihydrate, [Co(H₂O)₆](C₁₀H₈NO₃S)₂·2H₂O, (IV), crystallizes in a triclinic cell of similar dimensions, with the cations situated on centers of inversion. The overall packing is very similar to that of the Mn and Ni salts, with the main differences being the absence of the solvent water molecule on the special position and subtle modifications in the positioning of the anions within their layers. This series of salts is compared with those of the same metals with the 5‐aminonaphthalene‐2‐sulfonate and 4‐aminonaphthalene‐1‐sulfonate isomers, allowing for similarities and differences in packing to be discussed on the basis of the differing substitution of the naphthalene ring and, in some cases, differing degrees of hydration.     

Synthesis and Antitumor Evaluation of Some New Fused and Binary Pyridines

Syntheses of some new heterocyclic compounds containing pyridone, thioxopyridine, halogenated‐pyridine‐carbonitriles, pyrazolopyridine, and pyridine derivatives were achieved. Besides, a modified synthetic method for the synthesis of 2‐chloro‐4,6‐dimethyl‐nicotinonitrile ( 3 ) through the reaction of acetylacetone and malononitrile as starting materials was implemented. The reaction of 2‐chloronicotinonitrile 3 with substituted amines to 2‐aminonicotinonitrile were also investigated. Fused or binary pyridines were tested for cytotoxicity against well‐known established model Ehrlich ascites cells in vitro. Compound 13 exhibited a high antitumor activity compared with 5‐fluorouracil.     

Synthesis and photovoltaic properties of 2,6‐bis(2‐thienyl) benzobisazole and 4,8‐bis(thienyl)‐benzo[1,2‐B:4,5‐B′]dithiophene copolymers

In an effort to design efficient low‐cost polymers for use in organic photovoltaic cells the easily prepared donor–acceptor–donor triad of a either cis‐benzobisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole flanked by two thiophene rings was combined with the electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)‐thien‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (?5.2 to ?5.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from ?3.1 to ?3.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC₇₁BM ([6,6]‐phenyl C₇₁‐butyric acid methyl ester) as the acceptor, the trans‐benzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 316–324     

Reactivity Controlling Factors for an Aromatic Carbon‐Centered σ,σ,σ‐Triradical: The 4,5,8‐Tridehydroisoquinolinium Ion

The chemical properties of the 4,5,8‐tridehydroisoquinolinium ion (doublet ground state) and related mono‐ and biradicals were examined in the gas phase in a dual‐cell Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The triradical abstracted three hydrogen atoms in a consecutive manner from tetrahydrofuran (THF) and cyclohexane molecules; this demonstrates the presence of three reactive radical sites in this molecule. The high (calculated) electron affinity (EA=6.06 eV) at the radical sites makes the triradical more reactive than two related monoradicals, the 5‐ and 8‐dehydroisoquinolinium ions (EA=4.87 and 5.06 eV, respectively), the reactivity of which is controlled predominantly by polar effects. Calculated triradical stabilization energies predict that the most reactive radical site in the triradical is not position C4, as expected based on the high EA of this radical site, but instead position C5. The latter radical site actually destabilizes the 4,8‐biradical moiety, which is singlet coupled. Indeed, experimental reactivity studies show that the radical site at C5 reacts first. This explains why the triradical is not more reactive than the 4‐dehydroisoquinolinium ion because the C5 site is the intrinsically least reactive of the three radical sites due to its low EA. Although both EA and spin–spin coupling play major roles in controlling the overall reactivity of the triradical, spin–spin coupling determines the relative reactivity of the three radical sites.