Synthesis and thermolysis of heterocyclic 3-aza-3-ene-1,5-diynes(1)

[reaction: see text] Simple, acyclic 3-aza-3-ene-1,5-diynes undergo an aza-Bergman rearrangement to a fleeting 2,5-didehydropyridine (2,5-ddp) intermediate that rapidly ring-opens to beta-alkynylacrylonitrile products. In an effort to access longer-lived 2,5-ddp intermediates, we have prepared heterocyclic 3-aza-3-ene-1,5-diynes. The thermolysis of one such heterocyclic aza-enediyne does not afford products derived from trapping a 2,5-ddp intermediate but rather cyclopropanes that appear to arise from a carbene intermediate and a product that appears to be a trapping product from a 2,3-ddp intermediate.     

Multiple-electron transfer in a single step. Design and synthesis of highly charged cation-radical salts

[structure: see text]. Macromolecules 1c and 2c bearing multiple redox-active sites are synthesized by an efficient palladium-catalyzed coupling of 2,5-dimethoxytolylmagnesium bromide with readily available hexakis(4-bromophenyl)benzene and tetrakis(4-bromophenyl)methane. These macromolecular electron donors undergo reversible oxidation at a constant potential of 1.15 V vs SCE to yield robust, multiply charged cation radicals that are isolated in pure form using SbCl(5) as an oxidant. These nanometer-size cation-radical salts are shown to act as efficient "electron sponges" toward a variety of electron donors.     

One-electron oxidation of 1,3,5-triaryl-2-pyrazolines by antimony pentachloride

Upon reaction of 1,3,5-triphenyl- and 1,3,5-triphenyl-5-methyl-2-pyrazolines with antimony pentachloride in acetonitrile they undergo oxidation to cation radicals, which subsequently undergo rapid dimerization at the para positions of the N-phenyl groups. The final products are 4,4-bis(3,5-diphenyl-2-pyrazolin-1-ia)- and 4,4-bis(3,5-diphenyl-5-methyl-2-pyrazolin-1-ia)bis(cyclohexa-2,5-dienylidene) hexachloroantimonates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 551–554, April, 1985.     

Asymmetric synthesis of cis- and trans-2,5-disubstituted pyrrolidines from 3-oxo pyrrolidine 2-phosphonates: synthesis of (+)-preussin and analogs

Pyrrolidine enones, derived from 3-oxo pyrrolidine 2-phosphonates and a HWE reaction with aldehydes, on Luche reduction give pyrrolidine allylic alcohols. The alcohols on hydrogenation (Pd/H2) give cis-2,5-disubstituted pyrrolidines and on treatment with TFA-NaBH3CN undergo a hydroxy directed reduction to trans-2,5-disubstituted pyrrolidines.     

The exchange reaction of tetramethyl-diphosphine, -diarsine, -distibine and -dibismuthine

Tetramethyldiphosphine and tetramethyldiarsine undergo an exchange reaction to give (dimethylarsino)dimethylphosphine. The equilibrium constant at 25°C in benzene is found to be 0.26. Similarly, mixtures of tetramethyldistibine with tetramethyldiarsine or tetramethyldibismuthine are partially converted to (dimethylarsino)dimethylstibine or (dimethylbismuthino)dimethylstibine, respectively. The thermochromic arsinostibine, 1-(2,5-dimethylarsolo)-2,5-dimethylstibole, has been prepared by a similar reaction.     

Push-pull macrocycles: donor-acceptor compounds with paired linearly conjugated or cross-conjugated pathways

Two-dimensional π-systems are of current interest in the design of functional organic molecules, exhibiting unique behavior for applications in organic electronics, single-molecule devices, and sensing. Here we describe the synthesis and characterization of "push-pull macrocycles": electron-rich and electron-poor moieties linked by a pair of (matched) conjugated bridges. We have developed a two-component macrocyclization strategy that allows these structures to be synthesized with efficiencies comparable to acyclic donor-bridge-acceptor systems. Compounds with both cross-conjugated (m-phenylene) and linearly conjugated (2,5-thiophene) bridges have been prepared. As expected, the compounds undergo excitation to locally excited states followed by fluorescence from charge-transfer states. The m-phenylene-based systems exhibit slower charge-recombination rates presumably due to reduced electronic coupling through the cross-conjugated bridges. Interestingly, pairing the linearly conjugated 2,5-thiophene bridges also slows charge recombination. DFT calculations of frontier molecular orbitals show that the direct HOMO-LUMO transition is polarized orthogonal to the axis of charge transfer for these symmetrical macrocyclic architectures, reducing the electronic coupling. We believe the push-pull macrocycle design may be useful in engineering functional frontier molecular orbital symmetries.     

Absorption and fluorescence of 2,5-diarylidenecyclopentanones in acidic media: evidence for excited-state proton transfer

Spectroscopic properties for a series of 2,5-diarylidenecyclopentanones in weak and strong acid environments are reported. Electronic absorption and fluorescence spectra have been measured for the all-E configurations of 2,5-dibenzylidenecyclopentanone (1), 2,5-bis(3-phenylallylidene)cyclopentanone (2), and 2,5-bis(5-phenylpenta-2,4-dienylidene)cyclopentanone (3) in acetic acid and sulfuric acid solutions. The spectroscopic evidence indicates that in 96% sulfuric acid 1, 2, and 3 are protonated both in the ground state and on the S1 potential energy surface. This assignment is supported by Zerner's intermediate neglect of differential overlap (ZINDO) and time-dependent density functional theory (TD-DFT) calculations. In glacial acetic acid, 1, 2, and 3 are unprotonated in the ground state. The absence of observable fluorescence from 1 in glacial acetic acid indicates that S1 is npi, whereas the observation of fluorescence from 2 and 3 in acetic acid is consistent with S1 being pipi. A combination of spectroscopic data, molecular orbital calculations, and fluorescence lifetime measurements indicate that 2 and 3 undergo intermolecular excited-state proton transfer in glacial acetic acid and diluted sulfuric acid solutions. Photochemical studies reveal that, unlike its behavior in organic solvents, 1 does not undergo efficient E,E --> E,Z photoisomerization in 96% sulfuric acid.     

Novel design of 3,8-diazabicyclo[3.2.1]octane framework in oxidative sulfonamidation of 1,5-hexadiene

1,5-Hexadiene reacts with trifluoromethanesulfonamide in the oxidative system (t-BuOCl+NaI) to give trans-2,5-bis(iodomethyl)-1-(trifluoromethylsulfonyl)pyrrolidine 5 and 3,8-bis(trifluoromethylsulfonyl)-3,8-diazabicyclo[3.2.1]octane 6. With arenesulfonamides ArSO₂NH₂ (Ar=Ph, Tol), the reaction stops at the formation of the trans and cis isomers of 2,5-bis(iodomethyl)-1-(arenesulfonyl)pyrrolidine 7 and 8 (1:1). The cis isomers of 7 and 8 do not undergo cyclization to the corresponding 3,8-disubstituted 3,8-diazabicyclo[3.2.1]octanes. The reaction with triflamide represents the first example of one-pot two-step route to 3,8-diazabicyclo[3.2.1]octane system.     

Stereoselective synthesis of polysubstituted 2,5-dihydrofurans from reaction of 1,4-dilithio-1,3-dienes with aldehydes

[reaction: see text] Reaction of 1,4-dilithio-1,3-diene derivatives with 2 equiv of aldehydes affords polysubstituted 2,5-dihydrofurans in good to high yields with perfect regio- and stereoselectivities. Hexa-2,4-diene-1,6-dialcoholates are proposed as the first intermediates, which undergo a cyclization and subsequent elimination of Li(2)O to generate the 2,5-dihydrofuran derivatives.     

Facile synthesis and X-ray structure of alkoxy-functionalized dibenzo[fg,op]naphthacenes

[structure: see text] 1,3-Bis(2-bromophenyl)-2,5-diphenylbenzenes are readily available by the condensation of phenylacetates with the corresponding pyrylium salts and undergo a palladium-catalyzed dehydrohalogenation to give functionalized dibenzo[fg,op]naphthacenes.     

New tetrathiafulvalenes containing a 2,5-bis(thiophen-2-yl)pyrrole fragment: Synthesis, optical properties, and electrochemical behavior

The reaction of 1-(3-bromopropyl)-2,5-bis(thiophen-2-yl)-1H-pyrrole with cesium 5-methylsulfanyl-2-thioxo-1,3-dithiole-4-thiolate generated in situ gave previously unknown 4-{3-[2,5-bis(thiophen-2-yl)-1H-pyrrol-1-yl]propylsulfanyl}-5-methylsulfanyl-1,3-dithiole-2-thione, and cross-coupling of the latter with 4,5-disubstituted 1,3-dithiole-2-thiones in the presence of triethyl phosphite afforded new substituted tetrathiafulvalenes containing a 2,5-bis(thiophen-2-yl)pyrrole fragment. Optical properties and electrochemical behavior of the synthesized compounds were studied, and their ability to undergo electropolymerization was confirmed.     

Synthesis of γ-diketones by the method of conjugated hydrogenolysi s

Summary 1-Furylbutanol-3 and 1-furylpentanol-3 undergo conversions as the result of conjugated hydrogenolysis with hydrogenation in the vapor phase on skeletal Ni-Al at 240°-the former to hexanedione-2,5, heptanedione-2,5, and octanedione-2,5 in a total yield of 30%, the latter to heptanedione-2,5, octanedione-3,6 and nonanedione-3,6, in the same total yield.     

Synthesis and polymerization of sterically hindered 2,5-diphenyl- and 2,3,5-triphenyl-1-vinylpyrroles

Sterically hindered 2,5-diphenyl-and 2,3,5-triphenyl-1-vinylpyrroles have been obtained by the vinylation of the corresponding NH-pyrroles with acetylene in superbasic catalytic system KOH—DMSO in up to 78% yield. 2,3,5-Triphenyl-1-vinylpyrrole has also been obtained in 75% yield by the regioselective bromination of 2,3-diphenyl-1-vinylpyrrole with subsequent cross-coupling of 5-bromo-2,3-diphenyl-1-vinylpyrrole with phenylmagnesium bromide in the presence of dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium(II). 2,5-Diphenyl- and 2,3,5-triphenyl-1-vinylpyrroles undergo a free-radical polymerization (AIBN, 80 °C) to form oligomers in 11 and 27% yield, respectively.     

Synthesis and Photoinitiated Isomerizations of 3-(4-Nitrophenyl)-and 3-(4-Aminophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde and -2-carboxylic acid Derivatives

3-(4-Nitrophenyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde and its derivatives at the formyl group were synthesized. By reduction of the nitro group the corresponding 3-(4-aminophenyl)-substituted compounds were obtained, as well as 4,4'-bis(bicyclo[2.2.1]hepta-2,5-dien-2-yl)azobenzenes. Irradiation of the resulting norbornadiene derivatives in the region of their absorption maxima resulted in valence isomerization with formation of the corresponding quadricyclanes. The reverse transformations are promoted by molybdenum(VI) oxide as heterogeneous catalyst. 4,4'-Bis(bicyclo[2.2.1]hepta-2,5-dien-2-yl)azobenzenes undergo reversible (on heating) photochemical EZ/ isomerization at the NÍN bond.     

New strong organic acceptors by cycloaddition of TCNE and TCNQ to donor-substituted cyanoalkynes

Donor-substituted 1,1,2,4,4-pentacyanobuta-1,3-dienes and a cyclohexa-2,5-diene-1,4-diylidene-expanded derivative were prepared by a [2 + 2] cycloaddition of tetracyanoethene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) to anilino-substituted cyanoalkynes, followed by retro-electrocyclisation; they feature intense bathochromically-shifted intramolecular charge-transfer bands and undergo their first one-electron reductions at potentials similar to those reported for TCNE and TCNQ.     

New substituent effects of the trimethylsilyl group: photochemistry of 3-trimethylsilyl-2,5-cyclohexadienones and preparation of 4-alkylidenecyclopentenones

The 4-acetoxymethyl-4-alkyl-3-trimethylsilyl-2,5-cyclohexadien-1-ones 9a-g were prepared from methyl 2-trimethylsilylbenzoate by the Birch reduction-alkylation reaction. Type A photorearrangements of 9a-g were regiospecific to give mixtures of two diastereomers of the corresponding 5-trimethylsilylbicyclo[3.1.0]hex-3-en-2-ones 11a-g. These bicyclohexenones are uniquely photostable; the diastereomers do not photointerconvert nor do they undergo the type B photorearrangement. Bicyclohexenones 11a-g undergo acid-catalyzed protiodesilylative rearrangement to give the 4-alkylidene-2-cyclopenten-1-ones 25a-g. It was of interest to find that the 4-(3'-butenyl)-2,5-cyclohexadienone 9e photorearranged to the 5-trimethylsilylbicyclo[3.1.0]hex-3-en-2-one 11e rather than undergoing the intramolecular 2 + 2 photocycloaddition. Furthermore, the 4-acetoxymethyl-3-methoxy-4-methyl-5-trimethylsilyl-2,5-cyclohexadienone 30a did not show type A photobehavior at 366 and 300 nm, while the 4-(3'-butenyl) analogue 30b gave the intramolecular 2 + 2 cycloadduct 31b. The effects of the trimethylsilyl and methoxy substituents on the photochemical reactivity of 2,5-cyclohexadien-1-ones are discussed from the perspective of n --> p* vs pi --> p* character of the triplet states of the dienones.     

Pyrene‐Functionalised,Alternating Copolyimide for Sensing Nitroaromatic Compounds

A novel, pyrene‐functionalised copolymer has been synthesised in a single step via imidisation of poly(maleic anhydride‐alt‐1‐octadecene) with 1‐pyrenemethylamine, and its potential for the detection of volatile nitro aromatic compounds (NACs) evaluated. The new copolymer forms complexes in solution with NACs such as 2,5‐dinitrobenzonitrile, as shown by ¹H NMR, UV‐vis and fluorescence spectroscopy. Moreover, thin films of this copolymer, cast from THF solution, undergo almost instantaneous fluorescence quenching when exposed to the vapour of 2,5‐dinitrobenzonitrile (a model for TNT) at ambient temperatures and pressures.

     

Synthesis and photochromic properties of novel nonsymmetric dihetarylethenes based on benzindole and thiophene

Novel nonsymmetric dihetarylethenes 3-(5-methoxy-1,2-dimethyl-1H-benzo[g]indol-3-yl)-4-(3-thienyl)-furan-2,5-dione and 1-alkyl- and 1-aryl-3-(5-methoxy-1,2-dimethyl-1H-benzo[g]indol-3-yl-4-(3-thienyl)-1(H)-pyrrole-2,5-diones were synthesized. The substitution of the furandione moiety for pyrroledione gives rise to the radiation and photochemical channels of deactivation of the electron excitation energy of dihetarylethenes. The products of photolysis of pyrrolediones undergo recyclization in both the ground and excited states.     

Synthesis and thermolysis of tetrasubstituted cyclopropenes

Photolysis of 5-benzyl-2-methoxy-2,5-dimethyl-³-1, 3,4-oxadiazoline and of the 5,5-dibenzyl analogue with 300-nm light afforded 1-phenyl-2-diazopropane and 1,3-diphenyl-2-diazopropane, respectively. The diazoalkanes were intercepted, in situ, with dimethyl acetylenedicarboxylate to afford 3-benzyl-4,5-bis(methoxycarbonyl)-3-methyl-3H-pyrazole and 3,3-dibenzyl-4,5-bis(methoxycarbonyl)-3H-pyrazole, respectively. Those pyrazoles are short-lived under the reaction conditions and undergo two major reactions. Photolysis prior to rearrangement affords the corresponding 3,3-dialkyI-1,2-bis(methoxycarbonyl)-cyclopropenes. Thermal 1,5-benzyl migration converts the two 3H-pyrazoles in part into the corresponding 4H-pyrazoles, which undergo photolysis to 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropenes.Thermolysis of the 3,3-dialkyl-1,2-bis(methoxycarbonyl) cyclopropenes affords conjugated dienes, presumably through the sequence cyclopropene vinyl carbene diene. The stereochemistry of the dienes was determined and a mechanism consistent with that stereochemistry is proposed.The 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropanes are very stable under conditions that convert isomeric 3,3-dialkyl-1,2-bis(methoxycarbonyl)cyclopropenes to conjugated dienes. It is proposed that the effect of substitution pattern on the thermolysis rate constants is the result of combined ground state and transition state factors.     

Synthesis and Characterization of a Novel Lanthanide Complex with Photoluminescent and Semiconductive Properties

A novel lanthanide complex [La(2,5-PA)(2,5-HPA)(H₂O)₂]_n · nH₂O (I) (2,5-H₂PA = 2,5-pyridinedicarboxylic acid) was synthesized by a hydrothermal reaction and structurally characterized by singlecrystal X-ray diffraction (СIF file CCDC no. 1570808). Complex I is characteristic of a two-dimensional (2D) layered structure with the La₃+ ion coordinating with seven oxygen atoms and two nitrogen atoms to yield a slightly distorted monocapped square antiprism. The [La(2,5-PA)(2,5-HPA)(H₂O)₂]_n layers and lattice water molecules interlink together through hydrogen bonding interactions to give a three-dimensional (3D) supramolecular framework. Photoluminescence measurements under room temperature with solidstate samples show that it displays an emission in the green region of the light spectrum. Solid-state UV-Vis spectrum conducted with solid-state samples reveals the existence of a wide optical band gap of 3.57 eV.