Intramolecular diyl trapping reactions en route to the bicyclo [3.2.1] framework; an approach to aphidicolin

We describe an application of the intramolecular diyl trapping cycloaddition reaction to the assembly of the bicyclo [3.2.1] framework, and utilize the outcome to complete a formal total synthesis of aphidicolin.     

Polymer Light-emitting Diodes Based on End-capped Poly[9,9-di-(2'-ethylhexyl)fluorenyl-2,7-diyl]

We demonstrate polymer light‐emitting diodes (LEDs) based on poly[9,9‐di‐(2′‐ethylhexyl)fluorenyl‐2,7‐diyl] with end capper dimethylphenyl or N,N‐bis(4‐methylphenyl)‐N‐phenylamine. The introduction of end‐capper groups increased the device luminance and efficiency, while greatly depressing the green emission. For the devices constructed of poly[9,9‐di‐(2′‐ethylhexyl)fluorenyl‐2,7‐diyl] end capped with dimethylphenyl, the maximum luminance reached 381 cd/m² at 122 mA/cm². The maximum external quantum efficiency was 0.16% at 117 mA/cm², which is more than five times higher than that of the non‐end‐capped polymer LEDs. The electroluminescence (EL) maximum was at 485 nm, blue shifted by 52 nm with respect to that of the non‐end‐capped polyfluorene devices. It is proposed that efficient hole trapping at end capper and increased resistance of polyfluorene to oxidation are responsible for the improved device performance and color stability.     

Tandem retro-aldol/Wittig/Michael and related cascade processes

A number of novel tandem sequences initiated by a retro-aldol process are described along with preliminary scope and limitation studies. These include (i) retro-aldol/Wittig trapping/intramolecular Michael addition, (ii) retro-aldol/aza-Wittig/intramolecular imine addition, (iii) retro-aldol/Henry/intramolecular Michael addition and (iv) retro-aldol/Knoevenagel/intramolecular Michael addition sequences. A range of novel functionalised cyclopentanes, and related systems, are described which should prove to be useful synthetic building blocks.     

Tandem cycloaddition reactions of allenyl diazo compounds forming triquinanes via trimethylenemethane diyls

A tandem reaction strategy for forming triquinanes from linear allenyl diazo compounds through an intramolecular 1,3-dipolar cycloaddition reaction of an allenyl diazo group that generates a trimethylenemethane (TMM) diyl followed by an intramolecular [2 + 3] TMM diyl cycloaddition reaction has been developed. The new tandem cycloaddition reaction is readily applicable to the synthesis of complex molecules with high versatility and efficiency.     

From dimerization, to cycloaddition, to atom transfer cyclization: the further chemistry of TMM diradicals

We describe [a] the first examples of intramolecular cycloaddition of a TMM diyl to a remotely tethered aldehyde, [b] the effect of a Lewis acid upon the course of TMM chemistry, [c] examples of exclusive intramolecular cycloaddition, competitive cycloaddition and ATC, and exclusive ATC, and [d] a set of predictive guidelines with which to assess whether cycloaddition or ATC will be the preferred path, and when the two processes will be competitive. Remarkably, a wide variety of structures can be obtained simply by varying the length of the tether within the diazenes investigated. DFT calculations were used to probe the energy surfaces for both atom transfer and cycloaddition. The transition structure for atom transfer involving the captodative system indicates that it occurs earlier along the reaction coordinate than for a system having only one radical stabilizing group. This is consistent with the existence of an exothermic process leading from the initial diyl to the captodatively stabilized distonic diyl. Gratifyingly, theory agrees with observation and provides substantial insight into the chemistry.     

An alternative approach towards novel heterocycle-fused 1,4-diazepin-2-ones by an aromatic amidation protocol

The synthesis of new 1,4-diazepin-2-one derivatives starting from glycine or alanine aminoacids is presented. The key cyclization step includes the PIFA mediated formation of N-acylnitrenium ions and their subsequent intramolecular trapping by an (hetero)aromatic ring. The so-promoted aromatic amidation process takes place without loss of enantiomeric purity when optically pure methoxyamide precursors are employed.     

A hydrogen-bonding-modulated molecular rotor: environmental effect in the conformational stability of peptidomimetic macrocyclic cyclophanes

The conformational behavior of 16- to 18-membered ring peptidomimetic p-cyclophanes 1a,b-3a,b has been studied by NMR. The cycles bearing 16 and 17 atoms showed a dynamic process within the NMR time scale, produced by the rotation of the aromatic p-diphenylene moiety with respect to the macrocyclic main plane. The temperature dependence of 1H NMR spectra has been studied in order to get activation parameters of the energetic barrier for the process (VT-NMR and line shape analysis). The rate of the movement clearly depends on the macrocyclic ring size and the nature of the peptidomimetic side chain. Entropic and enthalpic contributions to the free energy of activation are discussed. The rotation of the aromatic ring is closely related to the intramolecular hydrogen bonding pattern, as suggested by temperature factors of NH chemical shifts (DeltadeltaNH/DeltaT) and molecular modeling. The interconnected roles of the solvation and the intramolecular H-bonds have been established by measurements (VT-NMR and DeltadeltaNH/DeltaT) in environments of different polarities and H-bonding abilities. We concluded that the conformational stability of the systems directly depends on the stability of the intramolecular H-bonding pattern. We finally showed how one of these peptidomimetics behaves as a methanol-dependent artificial molecular rotor. In this simple molecular device, the well-defined molecular rotation is tuned by the competition between intramolecular hydrogen bonds and interactions with the solvent.     

Electrochemical Reduction of 4,4′‐(2,2,2‐Trichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDT) and 4,4′‐(2,2‐Dichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDD) at Carbon Cathodes in Dimethylformamide

In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4′‐(2,2,2‐trichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4′‐(2,2‐dichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4′‐(ethene‐1,1‐diyl)bis(chlorobenzene) (DDNU) as principal product (67–94%), together with 4,4′‐(2‐chloroethene‐1,1‐diyl)bis(chlorobenzene) (DDMU), 1‐chloro‐4‐styrylbenzene, and traces of both 1,1‐diphenylethane and 4,4′‐(ethane‐1,1‐diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D₂O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon–chlorine bonds of DDT is a two‐electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products.     

Redox isomerization via azomethine ylide intermediates: N-alkyl indoles from indolines and aldehydes

Indolines react with aromatic and heteroaromatic aldehydes to yield N-alkyl indoles in a benzoic acid catalyzed redox isomerization reaction. Azomethine ylides are intermediates in this process which was established by intramolecular [3 + 2] trapping experiments.     

Photohole screening effects in polythiophenes with pendant groups

We compare two mechanisms that dominate the temperature-dependent changes in electronic structure for poly(3-hexylthiophene-2,5 diyl) (P3HT). Structural changes in the relative orientation and configuration of the aromatic ring backbone are observed to occur over a wide range in temperature and affect the local final state screening in photoemission. There are also changes in conductivity and carrier concentration at lower temperatures leading to altered long-range intramolecular screening of photoholes and final state effects that affect excitation spectroscopies including photoemission. For polyethylenedioxythiophene (PEDOT), temperature-dependent changes in the structure and configuration of the polymer backbone are not as significant, although temperature-dependent final state effects are observed.     

Divergence of carbonyl ylide reactions as a function of diazocarbonyl compound and aldehyde substituent: dioxolanes, dioxolenes, and epoxides

The products from dirhodium(II) acetate-catalyzed reactions between diazocarbonyl compounds and a series of benzaldehydes demonstrate the extent of competition between intramolecular and intermolecular trapping of carbonyl ylide intermediates and the electronic effects that govern these transformations. With dimethyl diazomalonate, competition exists between dioxolane and epoxide formation so that with p-anisaldehyde only epoxide formation is observed and with p-nitrobenzaldehyde only 1,3-dioxolane products are formed. With methyl diazoacetoacetate, intramolecular trapping of the intermediate carbonyl ylide results in the sole production of dioxolenes. However, the vinyldiazoacetate analogue of methyl diazoacetoacetate, as its tert-butyldimethlsilyloxy derivative, only produces epoxides in its reactions with substituted benzaldehydes.     

A metal-free approach to the synthesis of indoline derivatives by a phenyliodine(III) bis(trifluoroacetate)-mediated amidohydroxylation reaction

A novel approach to the synthesis of indoline derivatives is presented. The key cyclization step features the phenyliodine(III) bis(trifluoroacetate)- (PIFA-) mediated formation of a N-acylnitrenium ion and its succeeding intramolecular trapping by the olefin fragment. In addition, difunctionalization of the alkene moiety is achieved since the in situ generation of an additional hydroxy group at the terminal position of the original double bond accompanies the intramolecular C-N bond formation.     

Triquinanes from linear alkylidene carbenes via trimethylenemethane diyls

The intramolecular [2+3] cycloaddition reaction of the trimethylenemethane diyl generated from the intramolecular cyclopropanation reaction of alkylidene carbene produced linearly fused triquinanes regio- and stereoselectively. The current tandem cycloaddition reaction was applied to a 14-step total synthesis of hirsutene from methallyl alcohol.     

Conjugated Polymer Composite Nanoparticles by Rapid Mixing

Composite nanoparticles from poly[(9,9‐di‐n‐octylfluoren‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)] (F8BT) and poly(9,9‐di‐n‐hexylfluoren‐2,7‐diyl) (PF) with embedded inorganic nanoparticles (TiO₂, CdSe, and CdSe/CdS) are prepared through kinetic trapping by rapid turbulent mixing in a multi‐inlet vortex mixer without the need for polymer functionalization. High contents of inorganic materials up to 50–60 wt% are realized for all composites. The influence of flow ratios, sodium dodecyl sulfate (SDS) concentration, and absolute flow rates on the particle size and morphology is studied. High water‐to‐THF ratios and high total flow rates around 2 m s⁻¹ yield particle sizes below 50 nm. By adjusting these parameters, controlled particle sizes between 30 to several hundred nanometers are obtained. Composite particles from CdSe/CdS and F8BT or PF show a strong quenching of the polymer emission and near exclusive emission from the inorganic nanocrystal, which indicates an efficient energy transfer with fluorescence quantum yields of 23% for the F8BT/CdSe/CdS composites and 21% for the PF/CdSe/CdS composites. The dispersions are colloidally stable for several months.

     

Design and synthesis of new fluorescent probe for rapid and highly sensitive detection of proteins via electrophoretic gel stain

A new fluorescent molecular probe, 2,2′‐(1E,1′E)‐2,2′‐(4‐(dicyanomethylene)‐4H‐pyrane‐2,6‐diyl)bis(ethene‐2,1‐diyl)bis(sodium benzenesulfonate) salt ( 1 ), possessing the cyanopyranyl moieties and two benzene sulfonic acid groups was designed and synthesized to detect proteins in solution and for high‐throughput SDS‐PAGE. Compound 1 exhibited no fluorescence in the absence of proteins; however, it exhibited strong fluorescence on the addition of bovine serum albumin as a result of intramolecular charge transfer. Compared with the conventional protocols for in‐gel protein staining, such as SYPRO Ruby and silver staining, 1 achieves higher sensitivity, even though it offers a simplified, higher throughput protocol. In fact, the total time required for protein staining was 60–90 min under optimum conditions much shorter than that required by the less‐sensitive silver staining or SYPRO Ruby staining protocols. Moreover, 1 was successfully applied to protein identification by mass spectrometry via in‐gel tryptic digestion, Western blotting, and native PAGE together with protein staining by 1 , which is a modified protocol of blue native PAGE (BN‐PAGE). Thus, 1 may facilitate high‐sensitivity protein detection, and it may be widely applicable as a convenient tool in various scientific and medical fields.     

A stacked pyrazolo[3,4-d]pyrimidine-based flexible molecule: the effect on stacking of an ethyl group in comparison with a methyl group

In the crystal structure of 1,1′-(1,3-propane­diyl)­bis(5-ethyl-6-methyl­thio-4,5-di­hydro-1H-pyrazolo­[3,4-d]­pyrimidin-4-one), C₁₉H₂₄N₈O₂S₂, the pairs of pyrazolo­[3,4-d]­pyrimidine rings of the mol­ecule stack between the heterocyclic rings, due to intramolecular π–π interactions. The substituted ethyl and methyl groups are comparable as far as intramolecular stacking is concerned.     

Photoenolization of 2-(2-methyl benzoyl) benzoic acid, methyl ester: effect of E photoenol lifetime on the photochemistry

[reaction: see text] Photolysis of 3 in argon-saturated 2-propanol led to formation of 5 via intermolecular H-atom abstraction followed by lactonization. Irradiation of 4 in 2-propanol gave compounds 6 and 7 that also come from intermolecular H-atom abstraction. In contrast, photolysis of an oxygen-saturated solution of 3 in 2-propanol yields products 8, 9, and 10, which were all formed from intramolecular H-atom abstraction and trapping of the corresponding biradical with oxygen. Laser flash photolysis of 3 in methanol showed formation of biradical 3BR (lambda(max) 330 nm, and tau = 50 ns) via intramolecular H-atom abstraction as the main photoreactivity of 3. Biradical 3BR decayed into photoenols 3Z and 3E (lambda(max) 390 nm, tau = 6.5 micros and tau = 162 micros, respectively). In comparison, laser flash photolysis of 4 yielded photoenols 4Z and 4E (lambda(max) 390 nm, tau = 15 micros and tau = 3.6 ms, respectively). Thus photoenol 3E is unusually short-lived, and therefore it does not undergo the intramolecular lactonization as we have observed for the analogous photoenol 1E. Photoenol 3Z decays back to 3 via an intramolecular 1,5-H shift, whereas photoenol 3E reforms 3 efficiently via the solvent with the aid of the ortho ester group. The intramolecular lactonization of photoenols 1E and 3E must be a slow process, presumably because the photoenols are rigid and the hydroxyl group is inhibited, by intramolecular hydrogen bonding, from acquiring the correct geometry for lactonization. Thus only photoenols that are resistant to reformation of their ketone via the solvent are long-lived enough to undergo lactonization and release the alcohol moiety.     

Allenyl azide cycloaddition chemistry: exploration of the scope and mechanism of cyclopentennelated dihydropyrrole synthesis through azatrimethylenemethane intermediates

Detailed studies of the thermal conversion of 1-azidohepta-3,4,6-trienes into cyclopentennelated dihydropyrroles are presented. High levels of diastereoselectivity and regioselectivity are documented. A mechanistic proposal that accounts for all of the diverse results is developed through the use of density functional calculations. These calculations provide support for the intervention of unexpected mechanistic subtleties, such as the planarity of an azatrimethylenemethane diyl intermediate and an apparent Woodward-Hoffmann-type electrocyclization of a five-atom diyl array.     

Synthesis of spiro[pyrrolidine or piperidine-3,9′-xanthenes] by anionic cycloacylation of carbamates

Xanthene spiropyrrolidines and spiropiperidines were synthesized by a process in which the key step was intramolecular trapping of a xanthen-9-yl anion by a carbamate side-chain situated at the same position.     

Free Radical Cyclizations of Trienes with Tris(Trimethylsilyl)Silane

The intramolecular trapping of a stabilized intermediate allylic radical generated by the addition of tris(trimethylsilyl)silyl (sisyl) radical to a conjugated system was performed. The observed low stereoselectivity suggests thermodynamic rather than kinetic control in this cyclization process.