Unprecedented Scissor Effect of Macromolecular Cross-linkers on the Glass Transition Temperature of Poly(N-vinylimidazole), Crystallinity Suppression of Poly(tetrahydrofuran) and Molecular Mobility by Solid State NMR in Poly(N-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

Unexpected correlations have been found between structural parameters and glass transition temperatures (Tg) of poly(N-vinylimidazole) (PVIm) and crystallinity of poly(tetrahydrofuran) (PTHF) in a series of novel, unique PVIm-l-PTHF amphiphilic conetworks synthesized in broad composition ranges via free radical copolymerisation of VIm and semicrystalline, methacrylate-telechelic PTHF macromolecular cross-linkers with varying Mn from 2170 to 10 000 g mol−1. Differential scanning calorimetry (DSC) investigations revealed microphase separation between the covalently bonded PVIm and PTHF components, that is two distinct Tgs corresponding to the respective polymers (PVIm and PTHF) were obtained in these optically clear, transparent materials. Complete microphase separation, i.e. absence of mixed phases, was also confirmed by solid state NMR measurements. The Tg of the PVIm phase significantly decreases with increasing PTHF content, and Fox–Flory type correlation was surprisingly found between the Tg of PVIm and its Mc (average molecular weight between cross-links). This striking finding indicates a unique, unpredicted scissor effect of the macromolecular PTHF cross-linker in these materials, i.e. with respect to glass transition, PVIm behaves as individual chains between cross-links. The molecular mobility in the PVIm chain segments obtained by solid state NMR investigations shows a similar trend as a function of Mc. In the DSC thermograms, the semicrystalline PTHF has a sharp endothermic melting peak (Tm) indicating partial crystallisation of this polymer. It was found that the Tm and the crystalline fraction (Xc) of the PTHF phase are suppressed by even a minimal content of PVIm phase in the conetworks. Even complete diminishing of Xc occurs in conetworks with lower than 40 wt% PTHF of the lowest Mn (2170 g mol−1). Unexpectedly, Tm linearly decreases with Mc in conetworks with constant Mn of PTHF. These data indicate that the decrease of both Tm and Xc of PTHF is not only composition dependent, but the MW of the macromolecular PTHF cross-linker and the Mc of the PVIm component also have effects on these parameters. These results also indicate that chemical bonding of polymer chains in conetworks yields novel materials with unprecedented property variation. This provides unique opportunities for fine tuning of the investigated fundamental material properties, i.e. Tg, Tm and Xc, within certain ranges in the novel PVIm-l-PTHF amphiphilic conetworks by selecting the proper synthesis parameters, that is, composition and MW of the telechelic PTHF macromonomer cross-linker

Stereoselective Metal-Free Reduction of Chiral Imines in Batch and Flow Mode: A Convenient Strategy for the Synthesis of Chiral Active Pharmaceutical Ingredients

he convenient, metal-free reduction of imines that contain an inexpensive and removable chiral auxiliary allowed for the synthesis of the immediate precursors of chiral active pharmaceutical ingredients (APIs). This protocol was carried out under batch and flow conditions to give the correspoding prod- ucts in high yields with almost complete stereocontrol. In the presence of trichlorosilane, an inexpensive and nontoxic reduc- ing agent, and an achiral Lewis base such as N,N-dimethyl- Introduction The pharmaceutical industry is gradually progressing towards enantiopure formulations. Most newly introduced drugs are chiral, and it is expected that approximately 95 % of pharma- ceutical drugs will be chiral by 2020. [1] In this context, chiral amines are considered a class of paramount importance, be- cause they are found in a plethora of compounds such as those of pharmaceutical interest as well as those developed for agro- chemicals, fragrances, and fine chemicals. [2] The reduction of the C=N group is one of the most widely used approaches to synthesize chiral amines, and over the last ten years, successful catalytic enantioselective methods based on both metal-pro- moted [3] and organocatalyzed [4] strategies have been devel- oped. When an industrial synthesis of a chiral pharmaceutical prod- uct must be planned, however, issues such as the chemical effi- ciency and robustness of the procedure, its general applicabil- ity, and economic considerations become crucially important. For these reasons, the applications of many chiral catalytic sys- tems are often not feasible, and the use of inexpensive and readily available chiral auxiliaries becomes an attractive and economic alternative. This also holds true for the synthesis of [a] Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy E-mail: [email protected] http://users2.unimi.it/Benagliagroup [b] Istituto di Scienze e Tecnologie Molecolari ISTM-CNR, Via Golgi 19, 20133 Milano, Italy [c] Department of Chemistry and Chemistry Center of Évora, University of Évora, Rua Romão Ramalho, 59, 7000 Évora, Portugal Supporting information and ORCID(s) from the author(s) for this article are available on the WWW under http://dx.doi.org/10.1002/ejoc.201601268. Eur. J. Org. Chem. 2017, 39–44 © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim39 formamide, the formal syntheses of Rivastgmine, calcimimetic NPS R-568, and a Rho kinases inhibitor were successfully accom- plished. For the first time, both the diastereoselective imine re- duction and the auxiliary removal were efficiently performed in a micro- or mesoreactor under continuous-flow conditions, which paved the way towards the development of a practical process for the syntheses of industrially relevant, biologically active, enantiopure N-alkylamine

Evaluating the thermal vinylcyclopropane rearrangement (VCPR) as a practical method for the synthesis of difluorinated cyclopentenes : experimental and computational studies of rearrangement stereospecificity

Vinyl cyclopropane rearrangement (VCPR) has been utilised to synthesise a difluorinated cyclopentene stereospecifically and under mild thermal conditions. Difluorocyclopropanation chemistry afforded ethyl 3-(1'(2'2'-difluoro-3'-phenyl)cyclopropyl) propenoate as all four stereoisomers (18a, 18b, 22a, 22b) (all racemic). Trans-E isomer (18a), prepared in 70% yield over three steps, underwent near quantitative VCPR to difluorocyclopentene 23 (99%). Rearrangements were followed by 19F NMR (100-180 °C). While cis/trans cyclopropane stereoisomerisation was facile, favouring trans-isomers by a modest margin, no E/Z alkene isomerisation was observed even at higher temperatures. Neither cis nor trans Z-alkenoates underwent VCPR, even up to much higher temperatures (180 oC). Cis-cyclopropanes underwent [3,3]-rearrangement to afford benzocycloheptadiene species. The reaction stereospecificity was explored using electronic structure calculations and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment

Acute Large-Vessel Occlusion Masquerading as Traumatic Injury

A patient presented to an urban level 1 trauma center/accredited thrombectomy-capable stroke center for evaluation of suspected traumatic injury and was quickly determined to have symptoms suspicious for acute stroke that included dense hemiparesis with preserved mental status. He received a thrombectomy with an eventual return to neurologic baseline and discharge to acute inpatient rehabilitation 14 days after presentation

Cooperative effects involved in esterolytic reactions of cationic long chain esters catalyzed by benzimidazole-containing polymers

The solvolyses of positively charged esters with varying chain length catalyzed by benzimidazole, poly[5(6)-vinylbenzimidazole] and copolymers of 5(6)-vinylbenz-imidazole with acrylic acid were studied. Poly[5(6)-vinylbenzimidazole] showed a marked selectivity for the positively charged esters with varying aliphatic chain length but the catalytic activity was suppressed. In order to investigate the more detailed characteristics of the 5(6)-vinylbenzimidazole-acrylic acid copolymers in the solvolyses of these esters, the effects of copolymer composition on their catalytic activities were studied. In the solvolyses of every ester employed, the copolymer compositions affected their catalytic activities. In 40% 1-propanol-water the activities of the copolymers indicated a strong dependence on the carboxylatebenzimidazole-carboxylate triad. These effects were due to strong electrostatic interactions between these sequences and the substrates. The effects of solvent composition on the catalytic activities of the copolymer-catalyzed solvolyses were also investigated. The copolymers of 5(6)-vinylbenzimidazole with acrylic acid were found to have entirely different characteristics in methanol-water than in 1-propanol-water systems. The catalytic ability was found to be a function of the benzimidazole content and on the size of the substrate. Apolar interactions became a dominant force in the methanol-water system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22394/1/0000844.pd

The use of coal in a solid phase reduction of iron oxide

The results of the research process of producing metalized products by solid-phase reduction of iron using solid carbonaceous reducing agents. Thermodynamic modeling was carried out on the model of the unit the Fe-C-O and system with iron ore and coal. As a result of modeling the thermodynamic boundary reducing, oxidizing, and transition areas and the value of the ratio of carbon and oxygen in the system. Simulation of real systems carried out with the gas phase obtained in the pyrolys of coal. The simulation results allow to determine the optimal cost of coal required for complete reduction of iron ore from a given composition. The kinetics of the processes of solid-phase reduction of iron using coal of various technological brands

Synthesis and resolution of substituted pipecolic acids

A new general method for the preparation of 2-alkyl-pipecolic acids has been developed. The syntheses of 2-methyl-, 2-benzyl- and cis-6-methylpipecolic acids are described. (-)S- and (+)R-2-methylpipecolic acids were resolved by fractional crystallization of the quinine salt of their N-carbobenzoxy derivative. Isolation of (-)S-cis-6-methylpipecolic acid required the use of 4-phenylbenzyloxycarbonyl as protecting group to achieve selective crystallization of the quinine salt. The absolute configurations of these compounds were determined by circular dichroism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25448/1/0000898.pd

Conformational effects and cooperative interactions in poly[5(6)-vinylbenzimidazole]-catalyzed solvolyses of anionic, long-chain substrates

A new synthetic procedure for the monomer, 5(6)-vinylbenzimidazole, has been developed. Also, a new method for the formation of the benzimidazole moiety is reported. The monomer, 5(6)-vinylbenzimidazole, was subjected to a free radical solution polymerization and a solid state thermal polymerization. Poly[5(6)-vinyl-benzimidazole], prepared by the solution-free radical polymerization, was shown to be a linear addition polymer with pendant benzimidazole groups, whereas the thermally prepared polymer was shown to have a different structure. The solvolyses of negatively charged esters with varying aliphatic chain lengths catalyzed by poly[5(6)-vinylbenzimidazole] and compared to monomeric benzimidazole in 40% 1-propanol-water at 26[deg]C revealed that the polymer was more efficient and that its activity was a function of the degree of ionization. Neutral-neutral and neutral-anionic benzimidazole interactions are suggested. The polymer conformation was found to have a significant effect on the solvolysis reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22393/1/0000843.pd

Solvolysis of p-nitrophenyl esters catalyzed by oligo-4(5)-vinylimidazoles

The preparation of low molecular weight poly-4(5)-vinylimidazole is described. Oligomer fractions with molecular weight ranges from a few hundred to two thousand, five hundred were obtained by fractionation through a Sephadex LH-20 column. The apparent dissociation constant of the imidazolium ion in oligo-4(5)-vinylimidazole decreases rapidly as the average molecular weight increases from 390 to 626. At an average molecular weight greater than 626, the apparent dissociation-constant value plateaus. The imidazole group in oligo-4(5)-vinylimidazole with ca. 5 imidazole units per oligomer molecule shows 71% of the solvolytic rate of the imidazole groups which are located in the oligomer with an average molecular weight of 2460 during the solvolysis of p-nitrophenyl acetate. The results indicate that short-range imidazole groups are interacting with each other to catalyze the solvolysis of p-nitrophenyl acetate. Solvolysis of p-nitrophenyl heptanoate catalyzed by oligomer fractions in 21% (v/v) n-propanol-water solutions indicates that the solvolysis rate of p-nitrophenyl heptanoate increases with an increase of oligomer's molecular weight.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33570/1/0000071.pd

Hydrophilic polymers containing chiral nucleic acid base pendants as polynucleotide analogs

A survey of our recent work on synthetic polynucleotide analogs is given. Propionic acid and 3-methyl butyric acid derivatives substituted in the 2-position with nucleic acid bases have been used as chiral pendants for attachment to hydrophilic polyamine backbones. Hindered rotation about the amide bonds formed promotes a base-stacked structure as shown by ultraviolet hypochromic effects versus model compounds. If the pendant has been resolved, an optically active polymer results which may be studied by circular dichroism (CD). Thus, poly(ethylenimine) containing the (−)-2-(thymin-1-yl)-propionyl group as the grafted pendant showed exciton coupling of the B 2u transition of the base chromophores in the CD, as observed in polynucleotides. This implies at least a local helical order in the stacking. The biological activity of such structures is briefly discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46953/1/289_2004_Article_BF00254354.pd