Synthesis and characterization of novel polyimides from alicyclic dianhydride

New alicyclic Polyimides (PIs) were prepared from asymmetric alicyclic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) and the corresponding aromatic diamines such as p-phenylenediamine, m-phenylenediamine and oxydianiline etc. by the polycondensation in N-methyl-2-pyrrolidone (NMP) followed by chemical imidization as well as one step polyimidization in m-cresol in the presence of isoquinoline as a catalyst. The resulting PIs with glass transition temperatures ranging from 220 to 328 degrees C had the inherent viscosities within the range of 0.25 similar to 1.42 dL/g. These polymers were readily soluble in aprotic polar solvents such as NMP, dimethylacetamide (DMAc), dimethylesulfoxide (DMSO), etc. Furthermore, some of the polymers showed good solubility properties to common organic solvents like tetrahydrofurane and chlorform. Also, all of these polyimide films were tough, almost colourless, and transparent.

The reactivity of lanthanide alkyl compounds with phenylacetylene: Synthesis and structure of [(Bu(t)Cp)(2)LnC CPh](2) (Ln=Nd, Gd)

[(Bu(t)Cp)(2)LnCH(3)](2) (Ln = Nd, Gd) react with PhC=CH to form the dimeric alkynide-bridged complexes [(Bu(t)Cp)(2)LnC=CPh](2) [Ln = Nd (I), Gd (II)]. Both compounds crystallized from toluene in the monoclinic space group C2/c. The two complexes are homologous, composed of asymmetric metal-alkynide bridges with Nd-C, Gd-C (alkynide) bond lengths of 2.602(4), 2.641(5) (I) and 2.532(6), 2.601(7) Angstrom (II), respectively. The average Nd-C (ring) and Gd-C (ring) distances are 2.746(13) and 2.703(19)Angstrom.

Efficient heterogeneous asymmetric catalysis of the Mukaiyama aldol reaction by silica- and ionic liquid-supported Lewis acid copper(II) complexes of bis(oxazolines)

Lewis acid complexes based on copper(II) and an imidazolium-tagged bis(oxazoline) have been used to catalyse the asymmetric Mukaiyama aldol reaction between methyl pyruvate and 1-methoxy-1-tri-methylsilyloxypropene under homogeneous and heterogeneous conditions. Although the ees obtained in ionic liquid were similar to those found in dichloromethane, there was a significant rate enhancement in the ionic liquid with reactions typically reaching completion within 2 min compared with only 55% conversion after 60 min in dichloromethane. However, this rate enhancement was offset by lower chemoselectivity in ionic liquids due to the formation of 3-hydroxy-1,3-diphenylbutan-1-one as a by-product. Supporting the catalyst on silica or an imidazolium-modified silica using the ionic liquid or in an ionic liquid-diethyl ether system completely suppressed the formation of this by-product without reducing the enantioselectivity. Although the heterogeneous systems were characterised by a drop in catalytic activity the system could be recycled up to five times without any loss in conversion or ee.

A Synthesis of (S)-(-)-Umbelactone and Related α,β-Butenolides

The development of an asymmetric route for the synthesis of alpha,beta-butenolide building blocks, starting from commercially available D-mannitol, is described. The devised route was applied to a synthesis of the (S)-(–)-enantiomer of the antiviral natural product umbelactone, together with the construction of other synthetically useful lactone structures.

Total Synthesis of (+)-Azinothricin and (+)-Kettapeptin

Asymmetric total syntheses of (+)-azinothricin and (+)-kettapeptin have been completed through a common new pathway that exploits a highly chemoselective coupling reaction between the fully elaborated cyclodepsipeptide 5 and the glycal activated esters 3 and 4 at the final stages of both respective syntheses.

Total synthesis of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin: powerful new inhibitors of beta-catenin/TCF4-and E2F-mediated gene transcription

Herein we describe our asymmetric total syntheses of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin. We also demonstrate that molecules of this class powerfully inhibit beta-catenin/TCF4- and E2F-mediated gene transcription within malignant human colon cancer cells at low drug concentrations.

Asymmetric Carbon-Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes Immobilized using Supported Ionic Liquids

A series of bis(oxazoline) metal(II) complexes has been supported on silica and carbon supports by non-covalent immobilisation using an ionic liquid. The catalytic performance of these solids was compared for the enantioselective Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene and the Mukaiyama-aldol reaction between methyl pyruvate and 1-methoxy-1-trimethylsilyloxy-propene. In both reactions the enantioselectivity was strongly influenced by the choice of support displaying enantioselectivies (ee values) up to 40% higher than those conducted under homogeneous reaction conditions.

Time-dependent three-dimensional spectrum synthesis for Type Ia supernovae

A Monte Carlo code (artis) for modelling time-dependent three-dimensional spectral synthesis in chemically inhomogeneous models of Type Ia supernova ejecta is presented. Following the propagation of ?-ray photons, emitted by the radioactive decay of the nucleosynthesis products, energy is deposited in the supernova ejecta and the radiative transfer problem is solved self-consistently, enforcing the constraint of energy conservation in the comoving frame. Assuming a photoionization-dominated plasma, the equations of ionization equilibrium are solved together with the thermal balance equation adopting an approximate treatment of excitation. Since we implement a fully general treatment of line formation, there are no free parameters to adjust. Thus, a direct comparison between synthetic spectra and light curves, calculated from hydrodynamic explosion models, and observations is feasible. The code is applied to the well-known W7 explosion model and the results tested against other studies. Finally, the effect of asymmetric ejecta on broad-band light curves and spectra is illustrated using an elliptical toy model. © 2009 RAS.

A New Stereocontrolled Total Synthesis of the Mast Cell inhibitory Alkaloid, (+)-Monanchorin, via the Wittig Reaction of a Stabilized Ylide with a Cyclic Guanidine Hemiaminal

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An asymmetric total synthesis of the mast cell inhibitor (+)-monanchorin is reported in which a Sharpless AD on 11 and a cyclic sulfate ring opening with an azide feature as key steps. After further manipulation, a novel guanidine-controlled ester reduction provided the guanidine-hemiaminal 25 which underwent Wittig olefination to give 27. Hydrogenation and a second guanidine-controlled reduction of the ester in 28, to obtain aldehyde 29, then set up a trifluoroacetic acid mediated cyclization to give (+)-monanchorin TFA salt.

Total Synthesis of the Potent HIF-1 Inhibitory Antitumor Natural Product, (8R)-Mycothiazole, via Baldwin–Lee CsF/CuI sp3–sp2-Stille Cross-Coupling. Confirmation of the Crews Reassignment

A convenient asymmetric total synthesis of the potent HIF-1 inhibitory antitumor natural product, (−)- or (+)-(8R)-mycothiazole (1), is described. Not only does our synthesis confirm the 2006 structural reassignment made by Crews (Crews, P., et al. J. Nat. Prod. 2006, 69, 145), it revises the [α]_D data previously reported for this molecule in MeOH from −13.7° to +42.3°. The newly developed route to (8R)-1 sets the C(8)–OH stereocenter via Sharpless AE/2,3-epoxy alcohol reductive ring opening and utilizes two Baldwin–Lee CsF/cat. CuI Stille cross-coupling reactions with vinylstannanes 8 and 3 to efficiently elaborate the C(1)–C(4) and C(14)–C(18) sectors.

Synthesis of new vegetable oil-based polymeric materials

A crescente procura de recursos fosseis a que se tem assistido nos ultimos anos, tem resultado num crescimento sem precedentes dos precos, com consequencias imprevisiveis e que levara, no espaco de decadas, ao seu inevitavel esgotamento. A procura de um modelo de desenvolvimento sustentavel, baseado em recursos renovaveis e o grande desafio que se coloca a civilizacao no seculo XXI. A biomassa vegetal, atraves das designadas gBio-refinarias h, e uma alternativa logica para a producao de produtos quimicos e de materiais mas tambem de combustiveis e energia. Os oleos vegetais constituem uma das fracoes da biomassa vegetal, cuja exploracao tem merecido redobrada atencao nos ultimos anos, como fonte de materiais e de combustiveis. Assim, a presente dissertacao tem por objetivo o desenvolvimento de novos materiais polimericos derivados de oleos vegetais, seguindo duas abordagens distintas, nomeadamente a preparacao de polimeros atraves de polimerizacao por etapas e polimerizacao em cadeia (Parte B e C, respetivamente). Em primeiro lugar, foram sintetizados poliesteres alifaticos de cadeia longa a partir de monomeros provenientes do oleo de colza (Capitulo III). A auto-metatese do acido erucico com catalisadores de rutenio, seguida de hidrogenacao da ligacao dupla, originou o acido 1,26-hexacosanodioico, que por sua vez foi convertido em hexacosano-1,26-diol. Subsequentemente, a policondensacao do acido ƒ¿,ƒÖ-dicarboxilico de cadeia longa com o hexacosano-1,26-diol originou o poliester 26,26. O diacido C26 foi tambem polimerizado com outros alcano-diois de cadeia curta, nomeadamente o dodecano-1,12-diol e o butano-1,2-diol, produzindo, respetivamente, os poliesteres 12,26 e 4,26. Estes poliesteres de fontes 100% renovaveis possuem valores de Mn na ordem dos 8-14 kDa e valores de PDI entre 2.1 e 2.7. As propriedades destes poliesteres alifaticos foram avaliadas atraves de varias tecnicas, revelando elevada cristalinidade (com uma estrutura cristalina como a do polietileno) e elevadas temperaturas de fusao (74-104 ‹C), cristalizacao (68-92 ‹C) e degradacao (323-386 ‹C). Em segundo lugar, foram sintetizados polimeros lineares termo-reversiveis a partir de derivados do oleo de ricinio (Capitulo IV). Para tal foram preparados monomeros que incorporam aneis furanicos inseridos atraves do acoplamento tiol-eno, e que posteriormente foram polimerizados pela reacao de Diels-Alder (DA) entre os grupos furano (dieno A) e estruturas complementares do tipo maleimida (dienofilo B). Para as polimerizacoes DA foram consideradas duas abordagens diferentes, nomeadamente (i) o uso de monomeros com dois aneis furanicos terminais em conjunto com uma bismaleimida (sistemas AA+BB) e (ii) a utilizacao de um monomero que incorpora ambos os grupos reativos, furano e maleimida, na sua estrutura (sistema AB). Este estudo demonstrou claramente que ambas as estratégias foram bem sucedidas embora com diferentes resultados em termos da natureza dos produtos obtidos. Estes polímeros lineares apresentam valores relativamente baixos de Tg (-40 to -2 °C) devido à natureza flexível dos grupos separadores das funções reativas, e de Mn (4.5-9.0 kDa) dada a observada tendência de ciclização associada a concentrações baixas de monómero. A aplicação da reação de retro-DA aos polímeros em causa confirmou o seu caráter reversível, ou seja, a possibilidade de promover, em condições controladas, a despolimerização com recuperação dos monómeros de partida. Esta particularidade abre caminhos para materiais macromoleculares originais com aplicações promissoras tais como auto-reparação e reciclabilidade. Em terceiro lugar, sintetizaram-se polímeros não-lineares termo-reversíveis a partir de derivados do óleo de ricínio (Capítulo V). Para tal foram preparados monómeros trifuncionais e posteriormente polimerizados através da reação de DA entre os grupos reativos complementares furano/maleimida. Foram consideradas três abordagens distintas para preparar estes polímeros não-lineares, nomeadamente através da utilização de (i) um monómero bisfurânico em combinação com uma trismaleimida (sistema A2+B3) e (ii) um monómero trisfurânico em conjunto com uma bismaleimida (sistema A3+B2) que originaram materiais ramificados ou reticulados, e ainda (iii) a utilização de monómeros assimetricamente substituídos do tipo A2B ou AB2 capazes de originar estruturas macromoleculares hiper-ramificadas. Todos os sistemas apresentaram valores de Tg perto de 0 °C, o que era de esperar para estes materiais não-lineares. A aplicação da reação de retro-DA comprovou mais uma vez o caráter termo-reversível das polimerizações em causa. Em quarto lugar e último lugar, foram preparados copolímeros de acetato de vinilo (VAc) com monómeros derivados de óleo de girassol (Capítulo VI). Ésteres vinílicos de ácidos gordos (FAVE) foram sintetizados por transvinilação dos ácidos oleico e linoleico com VAc catalisada por um complexo de irídio. Os monómeros vinílicos preparados foram caracterizados e posteriormente homopolimerizados e copolimerizados com VAc através do uso dos grupos vinílicos terminais como função inicial de polimerização. A variação do tipo e quantidade de monómero FAVE e da quantidade de iniciador radicalar originou copolímeros de VAc com valores de Mn na gama de 1.2-3.0 kDa e valores de Tg de -5 a 16 °C. Os copolímeros foram avaliados em testes de cura oxidativa através das insaturações nas suas cadeias alifáticas para formar materiais reticulados, e os resultados sugerem que eles podem ser sistemas efetivos de cura para aplicações como tintas, vernizes e outros tipos de revestimento. Todos os materiais poliméricos preparados ao longo deste trabalho constituem contribuições atrativas para a área dos polímeros oriundos de recursos renováveis e representam uma prova indiscutível de que os óleos vegetais são percursores promissores de materiais macromoleculares com potenciais aplicações.

Attemped asymmetric dehydration with chiral carbodiimides /|nMin-jen Shiao. -- 260 0 St. Catharines [Ont. : s. n.],

This research work has been planned with the intention of synthesizing optically active bicyclo[3,l,0]-hexan-2-one using chiral carbodiimides. Several carbodiimides have been prepared for practice and for attempts at asymmetric induction. The total synthesis of dibenzo[e,g]- (l:3)diazonine and the partial synthesis of l:13-dimethyldibenzo[e,g]- (l:3)diazonine are reported. Attempts to resolve 6,6f-dimethyl-2,2t-diphenic acid were not successful. The NMR spectra of carbodiimides and the related thioureas are compared. The reaction transition state of the 4-hydroxycyclohexanone with optically pure R,R(+)-di(a-phenylethyl)-carbodiimide has been considered. The ORD application to chiral cyclohexanones is discussed.

Experimental and Computational Studies on Copper and Hydrobenzoin Derivatives in Catalytic Asymmetric Reactions

The use of theory to understand and facilitate catalytic enantioselective organic transformations involving copper and hydrobenzoin derivatives is reported. Section A details the use of theory to predict, facilitate, and understand a copper promoted amino oxygenation reaction reported by Chemler et al. Using Density Functional Theory (DFT), employing the hybrid B3LYP functional and a LanL2DZ/6-31G(d) basis set, the mechanistic details were studied on a N-tosyl-o-allylaniline and a [alpha]-methyl-[gamma]-alkenyl sulfonamide substrate. The results suggest the N-C bond formation proceeds via a cisaminocupration, and not through a radical-type mechanism. Additionally, the origin of diastereoselection observed with [alpha]-methyl-[gamma]-alkenyl sulfonamide arises from avoidance of unfavourable steric interactions between the methyl substituent and the N -protecting group. Section B details the computationally guided, experimental investigation of two hydrobenzoin derivatives as ligands/ catalysts, as well as the attempted synthesis of a third hydrobenzoin derivative. The bis-boronic acid derived from hydrobenzoin was successful as a Lewis acid catalyst in the Bignielli reaction and the Conia ene reaction, but provided only racemic products. The chiral diol derived from hydrobenzoin successfully increased the rate of the addition of diethyl zinc to benzaldehyde in the presence of titanium tetraisopropoxide, however poor enantioinduction was obseverved. Notably, the observed reactivity was successfully predicted by theoretical calculations.