Der zweistufige Carbanion-Mechanismus der Fragmentierung von 3-Aminopropylbenzoaten. Fragmentierungs-Reaktionen. 25. Mitteilung

The unsubstituted and p-substituted benzoates 2b – 2e of 3-dimethylamino-2,2bis(p-nitrophenyl)-propanol ( 2a ) undergo quantitative fragmentation in 80% ethanol yielding 1,1-bis(p-nitrophenyl)-ethylene ( 5 ) besides formaldehyde and dimethylamine, the hydrolysis products of the imonium ion 3 . The corresponding alcohol 2a , however, yields 2,2-bis(p-nitrophenyl)-ethanol ( 9 ) in addition to fragmentation products. Conversely, no fragmentation is observed with the benzoates 6b – 6e of 3-dimethylamino-2,2-diphenylpropanol ( 6a ) which lack electronwithdrawing substituents in the β-phenyl groups. These results are in agreement with a two-step carbanion mechanism (Scheme 2) involving the ionization of the aminoalkohol 2a and its esters 2b – 2e to the imonium ion 3 and the carbanions 4a – 4e . The latter undergo competitive cleavage, recombination and protonation to 5 , 2 and 9 , respectively, depending on the nucleofugal activity of –X. These conclusions are supported by the first-order rate constants for the benzoates 2b – 2e which differ merely by a factor of three. Since the p-substituents in the benzoate groups have only a minor effect on the reaction rate the bonds to the nucleofugal groups are not appreciably broken in the rate determining step.     

Efficient synthesis and properties of novel near-infrared electrochromic anthraquinone imides

An efficient synthesis of novel near-infrared electrochromic 6-substituted (NO2, Br) anthraquinone imides, i.e., 2a and 2b, was established. Bearing functional groups suitable for further structural modifications by nucleophilic substitution reaction and various metal-catalyzed coupling reactions (e.g., Suzuki coupling), 2a and 2b were easily transferred to 1a by reaction with 4-methoxyphenol and 1b by reaction with 4-hexyloxyphenylboronic acid, respectively. These new imides are electrochromic and absorb intensely in the near-infrared range of 700-1600 nm upon electrochemical reduction.     

Emission Turn‐On and Solubility Turn‐Off in Conjugated Polymers: One‐ and Two‐Photon‐Induced Removal of Fluorescence‐Quenching Solubilizing Groups

The synthesis of highly efficient two‐photon uncaging groups and their potential use in functional conjugated polymers for post‐polymerization modification are reported. Careful structural design of the employed nitrophenethyl caging groups allows to efficiently induce bond scission by a two‐photon process through a combination of exceptionally high two‐photon absorption cross‐sections and high reaction quantum yields. Furthermore, π‐conjugated polyfluorenes are functionalized with these photocleavable side groups and it is possible to alter their emission properties and solubility behavior by simple light irradiation. Cleavage of side groups leads to a turn‐on of the fluorescence while solubility of the π‐conjugated materials is drastically reduced.

     

Unravelling the reaction mechanism of the reductive ring contraction of 1,2-pyridazines

Substituted pyrroles may be synthesized from selected 1,2-pyridazines through a reductive ring contraction involving the addition of four electrons and four protons. Our density functional theory computations of this reaction mechanism show that the first reduction event must be preceded by the uptake of one proton by 1,2-pyridazine and that the reaction proceeds through a 2e(-)/3H(+)-bearing intermediate. In the absence of electron-withdrawing groups able to resonate charge away from the ring, this intermediate lies too high in energy, making the reaction sequence thermodynamically inaccessible. After another two-electron reduction and the addition of two more protons, the original 1,2-pyridazine ring opens. Ring contraction and ammonia elimination then proceed with very small barriers, irrespective of the substituents present in the original 1,2-pyridazine. By establishing the need for electron-withdrawing resonant groups in the 3- and 6-positions to stabilize the critical intermediate in the initial stages of the reaction, this work suggests that the scope of the reductive ring contraction of 1,2-pyridazines may be expanded to pyridazines bearing COCH(3) groups, amides or aryls in these positions. We also explain the lack of reactivity of unsubstituted 1,2-pyridazine and analyze the feasibility of bypassing the high energy 2e(-)/3H(+)-intermediate through disproportionation of earlier 2e(-)/2H(+)-bearing intermediates.     

Synthesis of Novel Carbosilane Dendrimers Based on Pentaerythritol

Novel pentaerythritol-based carbosilane dendrimers centered at carbon have been synthesised. Starting from tetraallyl ether based upon pentaerythritol as the core molecule, a succession of alternate Pt-catalyzed hydrosilylation of allyl groups with HSiC13 and allylations of SiC1 groups thus introduced with CH2=CHCH2MgBr in THF provided a divergent synthesis of three generations of carbosilane dendrimers in which the Si atoms are linked by CH2CH2CH2 groups. The reaction conditions for hydrosilylation must be well controlled. After purification by chromatography on silica gel pure products for each generation were obtained. The IR, ^1H and ^13C NMR spectra and elemental analysis data are consistent with the proposed structures. The molecular weights of the resulting carbosilne dendrimers have been determined by vapor pressure osmometry.     

Controlling the Scholl reaction

Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups (e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly. Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating m-directors (e.g., NO2) suppress reaction. MoCl5 and PhI(OOCCF3)2/BF3.Et2O are general and effective reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki-Miyaura couplings were used to generate 12 substituted o-terphenyl derivatives.     

Synthesis and characterization of poly[(3,4-dihydro-2h-pyran)-alt-(maleic anhydride)] and its derivatives: Biologically active polymers

The syntheses of several monomers, bioactive poly[(3, 4-dihydro-2H-pyran)-alt-(maleic anhydride)] and its derivatives, which have different substituents (e.g., acetoxy, methoxy, ethoxy, methoxycarbonyl, formyl, acetoxymethyl, and tosyloxymethyl groups) in the 2-position of the tetrahydropyran ring of the copolymer backbone, are described. The alternating sequences in copolymers of the dihydropyran derivatives and maleic anhydride were obtained from the equimolar and larger ratios of maleic anhydride to dihydropyran derivative at the onset of the copolymerization. The molecular weights of the copolymers were found to be low (M_n = 1000–7500) due to a transfer reaction of the dihydropyran derivatives. Hydrolyses of the anhydride groups in the copolymers without catalyst afforded poly[(dihydropyran)-alt-(maleic acid)] and its derivatives, whereas an additional three copolymers having substituents, e.g., hydroxy, hydroxymethyl, and carboxyl groups were obtained by hydrolyses of the pendent groups (acetoxy, acetoxymethyl, and methoxycarbonyl) with the aid of a hydroxide catalyst. Carbamoyl groups on the polymers were obtained from ammonolysis of methoxycarbonyl groups. The polymers having mercaptomethyl or aminomethyl groups were obtained by substitution of hydrogen sulfide or ammonia for tosyloxylmethyl groups.     

Cationic grafting from carbon black. VIII. Cationic ring-opening polymerization and copolymerization of oxepane initiated by acylium perchlorate groups on carbon black

The cationic ring-opening polymerization of oxepane was found to be initiated by carbon black having acylium perchlorate (CO⁺CIO) groups, which were introduced by the reaction of acyl chloride groups with silver perchlorate. It was confirmed that polyoxepane, i.e., poly(oxyhexamethylene), was propagated from CO⁺CIO groups on carbon black and effectively grafted on the surface. The rate of the polymerization and the percentage of grafting of poly(oxyhexamethylene) remarkably increased by the addition of epichlorohydrin (ECH) as a promoter: the percentage of grafting in the presence of ECH increased to about 100% with an increase in conversion. Furthermore, CO⁺CIO groups on carbon black have an ability to initiate the cationic ring-opening copolymerization of oxepane with ECH to give poly(oxepane-co-ECH) with various composition. The ring-opening copolymerization of oxepane with phthalic anhydride was also initiated by CO⁺CIO groups to give polyether ester, i.e., poly(hexamethylene phthalate) containing poly(oxyhexamethylene) sequence. In the copolymerization, polyether or polyether ester was effectively grafted from carbon black based on the propagation of these polymers from CO⁺CIO groups.     

Enhancement of Oxidative Stability of Polyfluorenes for Direct Thermal Lithography

A homopolymer of 9,9′‐bis[4‐(2‐(2‐tetrahydropyranyloxy)ethoxy)phenyl]fluorene and its copolymers with 3,4‐benzothiadiazole and 4,7‐di(3(4‐n‐octylphenyl)‐2‐thienyl)‐2,1,3‐benzothiadiazole were synthesized to produce a series of thermally reactive blue, green, and red luminescent polymers. Thermolytic removal of the tetrahydropyran (THP) group from polymer films, rendered the films insoluble due to the formation of hydroxyl groups on the termini of side chains. Thermal removal of the THP was lowered by up to 200 °C, when acid is present in the films. These polymers were found applicable to patterning by NIR direct thermal lithography, in conjunction with a NIR dye and thermal acid generator. The presence of the phenyl groups at the 9‐site carbon was found necessary to eliminate fluorenone formation, and enhance the colour purity of the material.

     

1,3-dimethoxy-5-methylene-1,3-cyclohexadiene compounds with leaving groups at C6: generation, solvolytic reactivity, and their importance in the photochemistry of 3,5-dimethoxybenzyl derivatives

The photochemistry of 3,5-dimethoxybenzyl compounds with the leaving groups acetate (1a), chloride (1b), bromide (1c), iodide (1d), diethyl phosphate (1e), and trimethylamine (1f), as the chloride, was examined by both product studies and flash photolysis. The isomeric triene, 5-methylene-1,3-cyclohexadiene derivative was observed for the acetate (2a), diethyl phosphate (2e) and trimethylammonium chloride (2f). The solvolysis of these derivatives, 2, was examined in alcohol solvents and the rate correlation with YOTS values gave m = 0.47 (2a) and 0.63 (2e), suggesting SN1 reactivity but with an early transition state. Quantum yields for formation of 2a and 2e indicated that these trienes play only a minor role (approximately 16%) in the overall photochemistry of the corresponding arylmethyl substrates.     

LiCl‐Mediated Preparation of Functionalized Benzylic Indium(III) Halides and Highly Chemoselective Palladium‐Catalyzed Cross‐Coupling in a Protic Cosolvent

Sensitive functional groups such as COR, CHO, or CH₂OH can be present in benzylic indium reagents prepared by the direct insertion of indium in the presence of LiCl. These reagents undergo palladium‐catalyzed cross‐coupling reactions in the presence of a protic cosolvent after activation with iPrMgCl⋅LiCl (see scheme). Remarkable chemoselectivities are achieved by using various electrophiles containing NH or OH groups.

     

Photoprocesses of molecules with 2-nitrobenzyl protecting groups and caged organic acids

The 308 nm photoinduced formation of the nitroso product and the intermediacy of the aci-nitro form(s) were studied for a series of 2-nitrobenzyl alkyl and aryl esters (1a-4e) and bis-(nitrophenyl)methyl acetates (5a-6b) by time-resolved UV-vis spectroscopy. A triplet state appears as major transient, when 2-nitrobenzyl derivatives 1 are substituted by 4,5-dimethoxy (2) and 4,5-methylenedioxy (3/4) groups. This triplet of charge transfer character is, however, not part of the route via the aci-nitro into the 2-nitroso form. The activation energy and preexponential factor of the longest lifetime component (tau(aci)), i.e. the major part of the aci-nitro decay, were determined. The carboxylic acids as leaving groups have rather small effects on tau(aci). An additional nitrated phenyl ring in alpha-position (5) leads generally to shorter tau(aci) value. Otherwise, the photogeneration of nitroso products is similar. The quantum yield (Phi(d)) varies only moderately with structure, the yield of the aci-nitro form and Phi(d) are correlated and little affected by solvent properties.     

Approach to the synthesis of indoline derivatives from diaryliodonium salts

An effective method of constructing the indoline moiety via intramolecular nucleophilic ring closure of a diaryliodonium salt is described. Diacetoxyiodoarene compounds (1a-1e) were converted into intermediate Koser's reagent and coupled with arylstannanes (7-10) to form diaryliodonium salts (11a-14e). Indoline compounds with different N-protecting groups, 15, 16, 17, and 18, were synthesized in higher yields by treating salts (11a-14e) with Cs(2)CO(3) and TEMPO. Regardless of the electronic environment of five para-substituted iodoarenes and the natures of four N-protected arylstannane groups, the conversion proceeded well to afford corresponding indolines in yields of 72-84 and 70-84%, respectively.     

Penicillamine disulfide (PNS) and alkaline cations

D-penicillamine disulfide (PNS) shows protolytic properties and is able to form complexes with cations, because it has two aminic groups and two carboxylic groups. The four protonation constants of its deprotonated species were determined by means of electromotive force (e.m.f.) measurements of a galvanic cell involving a glass electrode at 25 degrees C and in a constant ionic medium constituted by N(CH3)4Cl 3.00 or 1.00 mol dm-3. At 25 degrees C and in 3.00 mol dm-3 N(CH3)4Cl as ionic medium, equilibria taking place between PNS and lithium, sodium and potassium ions were investigated. Experimental data, again obtained from e.m.f. measurements, were explained by assuming the formation of species of the type MH2PNS ed M2H2PNS, where M indicates a cation. Stability constants for each proposed species were calculated. A comparison with cystine is discussed.     

Tailoring pore properties of MCM-48 silica for selective adsorption of CO2

Four different types of amine-attached MCM-48 silicas were prepared and investigated for CO(2) separation from N(2). Monomeric and polymeric hindered and unhindered amines were attached to the pore surface of the MCM-48 silica and characterized with respect to their CO(2) sorption properties. The pore structures and amino group content in these modified silicas were investigated by XRD, FT-IR, TGA, N(2) adsorption/desorption at 77 K and CHN/Si analysis, which confirmed that in all cases the amino groups were attached to the pore surface of MCM-48 at 1.5-5.2 mmol/g. The N(2) adsorption/desorption analysis showed a considerable decrease of the pore volume and surface area for the MCM-48 silica containing a polymeric amine (e.g., polyethyleneimine). The CO(2) adsorption rates and capacities of the amine-attached MCM-48 samples were studied employing a sorption microbalance. The results obtained indicated that in addition to the concentration of surface-attached amino groups, specific interactions between CO(2) and the surface amino groups, and the resultant pore structure after amine group attachment have a significant impact on CO(2) adsorption properties of these promising adsorbent materials.     

铑(I)催化的不对称硅氢化反应合成手性2-氨基-1-芳基乙醇研究

报道了以Rh()-手性2-(2-吡啶基)-4-羧甲基-1,3-噻唑烷为催化剂,2-氨基芳香酮的不对称硅氢化反应,在常温常压下手性2-氨基-1-芳基乙醇的产率几乎可达定量,产品光学纯度可达80%e.e以上.     

Synthesis of Poly(ethylene oxide)s Bearing Functional Groups along the Chain

Well‐defined poly(ethylene oxide)s (PEOs) bearing reactive sites regularly distributed along the chain have been synthesized by the polycondensation of PEO containing a central tertiary amino group with dichloromethane, followed by quaternization with suitable reagents to obtain polyzwitterionic or cationic PEOs with alkyl, allyl, or fluorocarbon pendant groups. The pendant allyl groups have been converted into primary amino groups by reaction with 2‐aminoethanethiol hydrochloride to obtain polyamino‐functionalized PEO.

Polyfunctional PEOs bearing different pendant groups.     

Synthesis of polymers with hydroxyl end groups by atom transfer radical polymerization

Polymers prepared by atom transfer radical polymerization (ATRP) contain end groups defined by the initiator used. Alkyl halides, used as initiators, lead to polymers with an alkyl group at one end and a halide as the other chain end. Using functionalized initiators such as 2‐hydroxyethyl 2‐bromopropionate, hydroxyl groups can be directly incorporated at one polymer chain end while the other end functionality remains a halogen. The direct displacement of the halogen end groups with hydroxyl groups was unsuccessful due to side reactions such as elimination (for polystyrene) or hydrolysis of ester functions (for polyacrylate). Another approach to generate hydroxyl end groups was based on the substitution of the halogen end groups by ethanolamine. This was successful for polystyrene but additional substitution at the backbone esters was observed in polyacrylates. Multiple substitution reactions could be avoided by using 4‐aminobutanol instead of 2‐aminoethanol. Hydroxyl terminated polyacrylates were also obtained by extending the polyacrylate chain end with one allyl alcohol unit in a one‐pot process by adding an excess of allyl alcohol at the end of e polymerization of acrylate.     

Asymmetric Syntheses Vi: Asymmetric Aldol Reaction of D-Camphor Imine Derived From Benzylamine

Addition of the D-camphor imine of benzylamine to a variety of aldehydes or ketones gives diastereose-lectivities ranging from 16–70%. The d.e. value is attributed by the difference of the orientation of C-11 groups. The rotation of (5e) indicates that addition reaction occurs from the pro-R face of lithium derivative (2).     

Cationic grafting from carbon black. II. Polymerization of styrene initiated by CO+ClO group on the surface of carbon black

The cationic grafting of polystyrene initiated by carbon black containing the CO⁺ClO group was investigated. The introduction of CO⁺ClO groups onto a carbon black surface was achieved by the reaction of AgClO₄ with carbon black that contained a COCI group. The latter was introduced by the reaction of carboxyl groups with SOCl₂. It was found that polystyrene chains could be grown from CO⁺ClO groups on the surface of carbon black. Moreover, polystyrene was effectively grafted from carbon black: the grafting ratio at 20°C increased to 58% as conversion increased. Furthermore, the grafting ratio and molecular weight of ungrafted polystyrene decreased with an increase in polymerization temperature. These results were explained by the fact that the increasing temperature of the polymerization caused an increase in the rate of chain transfer reaction of the growing polymer chain to the monomer. The carbon black obtained from the reaction produced a stable colloidal dispersion in a good solvent for polystyrene.