Vinyl Precursors Research Articles

Structure and isomerization behavior relationships of new push-pull azo-pyrrole photoswitches.

A family of stilbenyl-azopyrroles compounds 2a-d and 3a-d was efficiently obtained via a Mizoroki-Heck C-C-type coupling reaction between 2-(4'-iodophenyl-azo)-N-methyl pyrrole (1a) and different vinyl precursors. The influence of the π-conjugated backbone and the effect of the pyrrole moiety were correlated with their optical properties. Studies via UV-Visible spectrophotometry revealed that the inclusion of EWG or EDG favors a red-shift of the main absorption band in these azo compounds compared with their non-substituted analogues. Furthermore, there is a clear influence between the half-life of the Z isomer formed by irradiation with white light and the push-pull behavior of the molecules. In several cases, the stilbenyl-azopyrroles led to the formation of J-type aggregates in binary MeOH : H2O solvents, which are of interest for water compatible applications.

A comparative study on optical properties of pyrene-fused [4]helicenes and vinyl precursors

Polycyclic aromatic hydrocarbon-fused [n]helicene derivatives (PAH-fused [n]helicenes) have been widely investigated due to their excellent photoelectric and chiroptical properties. Herein, a series of pyrene-fused helicenes were synthesized by a photocyclization reaction and characterized by 1H/13C NMR spectroscopy and single crystal X-ray diffraction. All compounds and their vinyl precursors were studied as emitting materials. The experimental results reveal that these compounds possess reasonable emission efficiency (ΦFL = 97% for 3a) and tunable optical properties, and a wide emission band from bluish violet for 3c (401 nm) to green-yellow for 4c (530 nm) was observed. The detailed investigation indicated that an efficient, structure-controlled strategy was established to develop pyrene-based [n]helicene materials.

Living Cationic Ring-Opening Polymerization of Hetero Diels-Alder Adducts to Give Multifactor-Controlled and Fast-Photodegradable Vinyl Polymers.

Precise control of multiple structural parameters associated with vinyl polymers is important for producing materials with the desired properties and functions. While the development of living polymerization methods has provided a way to control the various structural parameters of vinyl polymers, the concomitant control of their sequence and regioregularity remains a challenging task. To overcome this challenge, herein, we report the living cationic ring-opening polymerization of hetero Diels-Alder adducts. The scalable and modular synthesis of the cyclic monomers was achieved by a one-step protocol using readily available vinyl precursors. Subsequently, living polymerization of the cyclic monomers was examined, allowing the synthesis of vinyl polymers while controlling multiple factors, including molecular weight, dispersity, alternating sequence, head-to-head regioregularity, and end-group functionality. The living characteristics of the developed method were further demonstrated by block copolymerization. The synthesized vinyl polymers exhibited unique thermal properties and underwent fast photodegradation even under sunlight.

Living Cationic Ring‐Opening Polymerization of Hetero Diels–Alder Adducts to Give Multifactor‐Controlled and Fast‐Photodegradable Vinyl Polymers

AbstractPrecise control of multiple structural parameters associated with vinyl polymers is important for producing materials with the desired properties and functions. While the development of living polymerization methods has provided a way to control the various structural parameters of vinyl polymers, the concomitant control of their sequence and regioregularity remains a challenging task. To overcome this challenge, herein, we report the living cationic ring‐opening polymerization of hetero Diels–Alder adducts. The scalable and modular synthesis of the cyclic monomers was achieved by a one‐step protocol using readily available vinyl precursors. Subsequently, living polymerization of the cyclic monomers was examined, allowing the synthesis of vinyl polymers while controlling multiple factors, including molecular weight, dispersity, alternating sequence, head‐to‐head regioregularity, and end‐group functionality. The living characteristics of the developed method were further demonstrated by block copolymerization. The synthesized vinyl polymers exhibited unique thermal properties and underwent fast photodegradation even under sunlight.

New cross-linked polysiloxanes prepared by UV-induced thiol-ene click-reaction

A series of new cross-linked polysiloxane polymers based on functionalized cyclo- and oligosiloxane precursors was prepared by UV-induced hydrothiolation “click”-reaction using DMPA as the initiator and their physico-mechanical properties were studied. The study of a morphology of prepared polymers by scanning electron microscopy (SEM) shows that the microstructure of all samples is homogenous. The mechanical properties of all the samples were studied by the tension and compression tests. It was shown that mechanical properties of studied materials, which significantly depends on precursors nature, can be fine-tuned by changing the structure of the initial vinyl precursor. The Young's modulus varies in the range of 4.5–117 MPa in the tension test and in the rage of 6.3–209 MPa in the compression test. The tensile strength varies in the range of 0.3–3.9 MPa in the tension test and in the rage of 2.3–28 MPa in the compression test. The thermal stability of the samples was evaluated by thermal gravimetric analysis (TGA). The weight loss was observed in the range of 275–333 °C in air and 322–370 °C in argon for prepared samples. All samples were characterized by DSC method. It was shown that only DSC curves for polymers 1 and 3 contain transitions related to glass formation (−78 and −35 °C, respectively). All polymer samples have a similar water contact angle in the range of 90–102°.

Phosphonium Tetraphenylborate: A Photocatalyst for Visible-Light-Induced, Nucleophile-Initiated Thiol-Michael Addition Photopolymerization.

A photoinitiation system that utilizes phosphonium tetraphenylborate as the key component was developed for the visible light-triggered nucleophile-catalyzed thiol-Michael addition reaction. This highly reactive catalyst was composed of a photocaged phosphine (methyldiphenylphosphonium tetraphenylborate, MDPP·HBPh4), a photosensitizer (isopropylthioxanthone, ITX), and a radical scavenger (TEMPO). Unlike the prevailing photobase catalysts, this photoactivatable phosphine system triggers the thiol-Michael addition polymerization by a nucleophile-catalyzed mechanism and provides a controlled stoichiometric reaction between the thiol and the vinyl precursors. This approach enables the formation of homogeneous polymer networks upon low-energy visible light exposure and, thus, broadens its potential applications in bulk polymer materials synthesis and UV-sensitive bioscaffold formation.

Heterotrimetallic complexes of iron and ruthenium based on vinyliminium dithiocarboxylate ligands

The diiron vinyliminium compounds [Fe2{μ-η1:η3-C(R2) = C(H)C=N(Me)R1}(μ-CO)(CO)(Cp)2]OSO2CF3 (R1 = Xyl = 2,6-C6H3Me2, R2 = Me; R1 = Me, R2 = CO2Me) provide a versatile entry point for many subsequent transformations, such as their reaction with carbon disulfide to provide zwitterionic dithiocarboxylate products. These compounds react with the coordinatively-unsaturated ruthenium vinyl precursors [Ru(CH=CHR3)Cl(CO)(PPh3)2] (R3 = C6H4Me-4, 1-Pyrenyl) to yield heterotrimetallic Fe2Ru compounds, exhibiting vinyl moieties at both iron and ruthenium centres. The emission associated with the pyrenyl unit is enhanced in the diiron vinyliminium ruthenium pyrenyl complex compared to the diethyldithiocarbamate analogue.

One‐pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography

A new vinyltrimethoxysilane-based hybrid silica monolith was developed and used as a reversed-phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, (29) Si nuclear magnetic resonance spectroscopy and N2 adsorption-desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m(2) /g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed-phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed-phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000).

Mild synthesis of mercaptonitriles from vinyl nitriles and their cyclization reactions

Thiol–ene addition of thioacetic acid A is widely used in the synthesis of thiols from vinyl precursors, but so far has not been conducted on non-conjugated vinyl nitriles.

Carbocyclic 4-Deazaformycins

The preparation of carbocyclic 4-deazaformycin and its 5′-homoanalogue from a common vinyl precursor, and its N-1 and N-2 methyl derivatives is reported. The syntheses began with a highly stereoselective SN2 reaction between lithio 4-picolines and a protected 2,3-dihydroxy-4-vinylcyclopentyl triflate. The requisite fused pyrazole ring was created by an intramolecular diazonium reaction that was followed by vinyl transformation into the hydroxymethyl and the hydroxyethyl groups. The N-methyl derivatives arose by standard methylation conditions and the resultant N-Me regiochemistry was assigned by homo- and heteronuclear NMR spectroscopy.

Polymer Surface Processing by Atmospheric Pressure DBD for Post-Discharge Grafting of Washing-Resistant Functional Coatings

We present a process for rapid post-discharge deposition of liquid monomer to form functional coatings at atmospheric pressure. The post-discharge polymerization of dense polyacid and polyether coatings is first depicted versus the energy density deposited by the preliminary surface treatment of polyethylene and polystyrene substrates in air Dielectric Barrier Discharge (DBD) with respect to SEM, to XPS and FTIR-ATR analysis and to polymerization yield determined by mass measurements. The paper focuses on the effect of the filamentary air DBD on surface of the polymer substrates and on post-discharge polymerization mechanism. Indeed, the grafting yield is shown to depend on the energy density deposited by DBD and on the time exposure to air between DBD and monomer deposition, controlling respectively the surface density of radicals and labile peroxides, both triggering the polymerization of vinyl precursors. Then, the effect of deposition conditions on the polymerization yield and related thickness of the functional polymer coatings is shown and special attention is paid to the stability of the coating upon washing.

Grafting and Polymer Formation on Silicon from Unsaturated Grignards: II. Aliphatic Precursors

Anodic decomposition of a vinylmagnesium halide or an ethynylmagnesium halide at a surface-hydrogenated silicon electrode leads to the formation of polymeric layers covalently anchored to the silicon surface. These layers have been characterized using spectroellipsometry and photoluminescence, infrared, and X-ray photoelectron spectroscopy. In the case of vinyl precursors, it appears that the multiple bonds are largely broken in the process. In the case of ethynyl, the layer formation rate is much higher for the chloride than for the bromide. The obtained polymer appears as a saturated skeleton bearing halide and unsaturated ethynyl groups. Furthermore, it appears that the solvent may be attacked by the ethynyl radicals leading to contamination of the polymer by solvent fragments, an effect that can largely be avoided by using appropriate solvents. The reaction pathways are discussed.

Synthesis and radioiodination of 3-(E)-(2-iodovinyl)-N-acetyl-4-cysteaminylphenol, a putative tyrosinase substrate for imaging neural crest tumours

The synthesis of 3-(E)-(2-iodovinyl)-N-acetyl-4-cysteaminylphenol (3-IV-N-Ac-4-SCAP) started from 3-iodophenol, which on condensation with cysteamine hydrochloride gave 3-iodo-4-cysteaminylphenol (1). Acetylation of 1 followed by selective deacetylation yielded 3-iodo-N-acetyl 4-cysteaminylphenol (3-I-N-Ac-4-SCAP; 3). The stereospecific reaction of (E)-1-trimethylsilyl-2-tri-n-butyltinethylene with 3 afforded the vinyl-TMS precursor 3-(E)-(2-trimethylsilylvinyl)-N-acetyl-4-cysteaminylphenol (3-TMS-N-Ac-4-SCAP; 4) in high yield. This TMS vinyl precursor is a useful synthon for high specific radioiodination. Iodination of the synthon 3-(E)-(2-trimethylsilylvinyl)-N-acetyl-4-cysteaminylphenol with iodine monochloride gave 3-IV-N-Ac-4-SCAP (5). High specific activity (no carrier added) 3-(E)-(2-[125I]iodovinyl)-N-acetyl-4-cysteaminyl phenol was obtained in 85% radiochemical yield upon a 5 min exposure of a mixture of Na[125I]I and 3-TMS-N-Ac-4-SCAP to 2450 MHz radiation in a microwave oven. © 1998 John Wiley & Sons, Ltd.

An efficient route to vinylporphyrins

The use of 1-bromo-19-methylbiladienes-ac in the synthesis of vinylporphyrins is described. The effect of the vinyl precursors on the reactions of the dipyrromethene intermediates and the construction of the linear tetrapyrrole are discussed. High-yield syntheses of a methylvinylporphyrin, an H-vinyl analogue, as well as two A,C-divinylporphyrins are presented. Keywords: pyrrole, dipyrromethene, acetoxyethylpyrrole, chloroethylpyrrole, biladiene-ac, porphyrin, vinylporphryin, benzoporphyrin, decarboxylation, transesterification.

Convenient synthesis of 10-deazaaminopterin via a pteridine ylide.

10-Deazaaminopterin, a potential antitumor agent now undergoing clinical trials, has been synthesized by a new approach involving the Wittig reaction. The ylide obtained by reaction of 6-(bromomethyl)-2,4-pteridinediamine with triphenylphosphine in Me2NAc, followed by treatment with NaOMe, underwent smooth reaction with diethyl N-(4-formylbenzoyl)-L-glutamate to give the vinyl precursor of the subject compound. Catalytic hydrogenation (Pt in glacial AcOH) of this product at ambient conditions led to uptake of 3 molar equiv of H2. Exposure to air during saponification of the ester groupings apparently gave the 7,8-dihydro compound according to UV spectral data, and further oxidation with H2O2 led to 10-deazaaminopterin.