Synthesis, Structure, and Nonlinear Optical Properties of Cross-Conjugated Perphenylatediso-Polydiacetylenes

Density Functional Theory Study on the Mechanism of Nickel-Catalyzed 3,3-Dialkynylation of 2-Aryl Acrylamides Via Double Vinylic C-H Bond Activation

The mechanisms of Ni-catalyzed 3,3-dialkynylation of 2-aryl acrylamide have been investigated by using density functional theory calculations. The result shows that this reaction includes double alkynylation, which involves sequential key steps of vinylic C-H bond activation, successive oxidative addition, and reductive elimination, with the second C-H bond activation being the rate-determining step. C-H and N-H bond activation occurs via the concerted metalation-deprotonation mechanism. The calculations show that no transition state exists in the first reductive elimination process, and a negative free energy barrier in the second reductive elimination process though a transition state is identified, indicating that the nickel-catalyzed vinylic C(sp2)-C(sp) bond formation does not require activation energy. Z-E isomerization is the prerequisite for the second alkynylation. In addition, our spin-flip TDDFT (SF-TDDFT) computational result discloses that the actual process of Z-E isomerization occurs on the potential energy surface of the first excited singlet state S1.

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

A set of novel 1,4-diaryl-1,3-butadiynes terminated by two 7-(arylethynyl)-1,8-bis(dimethylamino)naphthalene fragments was prepared via the Glaser-Hay oxidative dimerization of 2-ethynyl-7-(arylethynyl)-1,8-bis(dimethylamino)naphthalenes. The oligomers synthesized in this way are cross-conjugated systems, in which two conjugation pathways are possible: π-conjugation of 1,8-bis(dimethylamino)naphthalene (DMAN) fragments through a butadiyne linker and a donor-acceptor aryl-C≡C-DMAN conjugation path. The conjugation path can be "switched" simply by protonation of DMAN fragments. X-ray diffraction, UV-vis spectroscopy and cyclic voltammetry are applied to analyze the extent of π-conjugation and the efficiency of particular donor-acceptor conjugation path in these new compounds. X-ray structures and absorption spectra of doubly protonated tetrafluoroborate salts of the oligomers are also discussed.

Fused diethynylbenzenes and phenanthrenes via arynes with alkynylsilanes

A method for the hydroalkynylation and catalytic cyclization reactions of hexadehydro-Diels-Alder-derived benzynes is described. Diethynylbenzene derivatives are generated in a one-step reaction via trimethylsilyl-alkyne groups with benzyne formed by heating the appropriate tetrayne substrate. Trimethyl(phenylethynyl)silane loses TMS and binds to the electron-deficient site on HDDA-derived benzynes, and then phenanthrene was synthesized under mild reaction conditions by transition-metal-free, base promoted intramolecular cyclization.

Nickel-Catalyzed 3,3-Dialkynylation of 2-Aryl Acrylamides: Direct Access to gem-Diethynylethenes via Double Vinylic C-H Bond Activation

Direct access to gem-diethynylethenes is achieved by a Ni-catalyzed 3,3-dialkynylation of 2-aryl acrylamides with 1-bromotriisopropylsilylacetylene. The preliminary mechanism study reveals that the reaction goes through a sequential double vinylic C-H bond activation with the assistance of an 8-aminoquinolinyl directing group.

Anti-Inflammatory, Antioxidant, and Anthelmintic Activities of Ocimum basilicum (Sweet Basil) Fruits

Basil (Ocimum basilicum Linn.) is a plant that has found use in traditional medicine and household remedy against human ailments. The present study aimed at investigating hexane and ethanol fruit extracts of Ocimum basilicum Linn. for their phytoconstituents and anti-inflammatory, antioxidant, and anthelmintic activities. Phytochemical screenings were performed using standard protocols. Anti-inflammatory activities were assessed using the egg albumin denaturation method, while the antioxidant activities of the extracts were determined using DPPH scavenging, total antioxidant capacity (TAC), and hydrogen peroxide (H2O2) assays. In vitro anthelmintic activity of both extracts was investigated against Eudrilus eugeniae (Earthworms). Column chromatography was employed to separate the least polar fraction A, using hexane as the mobile phase, which was analyzed using FTIR analysis. The preliminary phytochemical screening revealed the presence of alkaloids, phenols, saponins, glycosides, steroids, tannins, terpenoids, and flavonoids. The hexane and ethanol extracts exhibited high concentration-dependent anti-inflammatory activities, with their percentage inhibitions being 34.0 ± 0.01 and 17.6 ± 0.04 μg/mL, respectively. The hexane extract showed a higher concentration-dependent antioxidant activity (IC50 of 14.17 ± 1.15 μg/mL) compared to the ethanol extract (IC50 > 100.0 μg/mL) for the DPPH assay. The IC50 values of ethanol and hexane extracts were 623.5 ± 0.27 and >1000.0 μg/mL, respectively, for the H2O2 scavenging assay. TAC was determined to be 37.48 ± 0.09 and 18.81 ± 0.12 gAAE/100 g for ethanol and hexane extracts, respectively. Both extracts showed a higher concentration-dependent anthelmintic activity. Increasing the concentration increased the helmintic potency of the extracts. The results indicate that both hexane and ethanol extracts of Ocimum basilicum Linn. exhibit anti-inflammatory, antioxidant, and anthelmintic activities and support the traditional usage of this plant.

Synthesis and Properties of 2,3-Diethynyl-1,3-Butadienes

The first general preparative access to compounds of the 2,3-diethynyl-1,3-butadiene (DEBD) class is reported. The synthesis involves a one-pot, twofold Sonogashira-type, Pd⁰ -catalyzed coupling of two terminal alkynes and a carbonate derivative of a 2-butyne-1,4-diol. The synthesis is broad in scope and members of this structural family are kinetically stable enough to be handled using standard laboratory techniques at ambient temperature. They decompose primarily through heat-promoted cyclodimerizations, which are impeded by alkyl substitution and accelerated by aryl or alkenyl substitution. An iterative sequence of these unprecedented Sonogashira-type couplings generates a new type of expanded dendralene. A suitably substituted DEBD carrying two terminal alkyne groups undergoes Glaser-Eglinton cyclo-oligomerization to produce a new class of expanded radialenes, which are chiral due to restricted rotation about their 1,3-butadiene units. The structural features giving rise to atropisomerism in these compounds are distinct from those reported previously.

ppm Pd-catalyzed, Cu-free Sonogashira couplings in water using commercially available catalyst precursors

A new catalyst that derives from commercially available precursors for copper-free, Pd-catalyzed Sonogashira reactions at the sustainable ppm level of precious metal palladium under mild aqueous micellar conditions has been developed. Both the palladium pre-catalyst and ligand are commercially available, bench stable, and highly cost-effective. The catalyst is applicable to both aryl- and heteroaryl-bromides as educts. A wide range of functional groups are tolerated and the aqueous reaction medium can be recycled. An application to a key intermediate associated with an active pharmaceutical ingredient (ponatinib) is discussed.

Synthesis, characterization, and solid-state polymerization of cross-conjugated octatetraynes

Two series of cross-conjugated 1,3,5,7-octatetraynes (1a–1l and 6a–6d) have been synthesized. UV–vis spectroscopic analysis shows that pendent groups connected to the cross-conjugated skeleton have little effect on the λmax energies, irrespective of whether the groups are electron withdrawing or donating. A number of the isolated products readily give crystals suitable for X-ray crystallography, and the solid-state structural properties of five derivatives (1k, 1l, 6a, 6c, and 6d) have been examined by X-ray crystallographic analysis. Parallel packing of the polyynes in the solid state indicates that four of the five samples are potentially suitable for topochemical polymerization, based on solid-state packing parameters θ, R, and d. Attempts to effect a solid-state reaction have been explored through UV–vis and γ-ray irradiation as well as thermal heating. The course of these reactions was monitored by differential scanning calorimetry (DSC) analysis, as well as UV–vis and solid-state 13C NMR spectroscopy (for 1d, 1j, 1k, and 6d), which offered evidence of polymer formation from these reactions. Structural determination of the product(s), however, remains elusive.

Controlling the conformational changes in donor-acceptor [4]-dendralenes through intramolecular charge-transfer processes

The synthesis of two [4]-dendralene compounds incorporating thiophene-(p-nitrophenyl) donor-acceptor units is presented. The dendralenes adopt two different conformers in solution and solid state and the transformation between the structures can be controlled by light and heat. The electron-donating components of the dendralenes are represented by bromothienyl (in 13) and ethylenedioxythiophene(EDOT)-thienyl (in 15) end-groups. The most facile transformation involves the isomerisation of donor-acceptor conjugated systems (a conformers) into structures in which only the thiophenes are conjugated (b conformers), and this process is driven by ambient light. The structures of the two conformers of compound 13 are confirmed by single-crystal X-ray diffraction studies and the structural changes in both compounds have been monitored by 1H NMR spectroscopy and absorption studies. The transformations were found to be first-order processes with rate constants of k=0.0027 s(-1) and k=0.00022 s(-1) for 13 and 15, respectively. Density functional theory calculations at the B3LYP/6-31G* level give credence to the proposed mechanism for the a-->b conversion, which involves photoinduced intramolecular charge transfer (ICT) as the key step. The EDOT derivative (15) can be polymerised by electrochemical oxidation and a combination of cyclic voltammetry and UV/Vis spectroelectrochemical experiments indicate that the a conformer can be trapped and stabilised in the solid state.

Expanded radialenes: Modular synthesis and properties of cross-conjugated enyne macrocycles

During the past two decades, shape-persistent conjugated macrocycles with a broad spectrum of attributes and topologies have been synthesized. This includes macrocycles with remarkable electronic, optical, and supramolecular properties, as well as intriguing frameworks. Expanded radialenes are a class of conjugated shape-persistent macrocycles that arise from the formal insertion of acetylene units into a radialene framework. A related class of macrocycles, the expanded radiaannulenes, contains both endo- and exocyclic vinylene and vinylidene segments, respectively, and accordingly exhibits properties intermediate between radialenes and annulenes. Enyne building blocks have been developed that are suitable for forming a macrocyclic framework through a step-wise sequence of Pd-catalyzed cross-coupling reactions. This "building-block" approach allows us to explore a range of molecular architectures that will ultimately provide for an understanding of π-delocalization in these compounds. The synthesis and structural characterization of the first members of this new class of expanded radialenes and radiaannulenes are described.

Synthesis and Optical Properties of Bis(oligophenyleneethynylenes)

Bis(oligophenyleneethynylenes) 1-4 were prepared as representative members of a new class of potential nonlinear optical materials. The optical properties of 1-4 were examined for evidence of restricted rotation of the aryl rings when compared to their single-strand precursors, which could potentially increase their nonlinear response through more effective conjugation. The effect of altering the electron density of the terminating functional group of these compounds on their properties was also investigated.

Chiral, cross-conjugated isopolydiacetylenes

A series of chiral, monodisperse enyne oligomers (isopolydiacetylenes) based on a 1,1-binaphthyl core has been synthesized and characterized spectroscopically.