Chemoenzymatic synthesis of chiral 4,4 '-bipyridyls and their metal-organic frameworks

The first enantiopure 4,4'-bipyridyls, 6, 8, and 9 have been prepared in four or five steps via bacterial dioxygenase-catalysed cis-dihydroxylation of 4-chloroquinoline 1 and C-C coupling; ligands 6 and 9 are found to be effective building blocks for the preparation of chiral metal-organic frameworks as demonstrated with the rational synthesis of two pillared-grid structures [Zn-2(fumarate)(2)(L)], which exhibit interesting structural and dynamic aspects.

Chemoenzymatic synthesis of chiral 2,2 '-bipyridine ligands and their N-oxide derivatives: applications in the asymmetric aminolysis of epoxides and asymmetric allylation of aldehydes

A series of enantiopure 2,2'-bipyridines have been synthesised from the corresponding cis-dihydrodiol metabolites of 2-chloroquinolines. Several of the resulting hydroxylated 2,2'-bipyridines were found to be useful chiral ligands for the asymmetric aminolysis of meso-epoxides leading to the formation of enantioenriched amino alcohols (-> 84%ee). N-oxide and N,N'-dioxide derivatives of these 2,2'-bipyridines, including separable atropisomers, have been synthesised and used as enantioselective organocatalysts in the asymmetric allylation of aldehydes to give allylic alcohols (-> 86%ee).

New pinene-derived pyridines as bidentate chiral ligands

A synthesis of new bidentate pyridines has been developed, starting from ?-pinene. A copper complex of the pyridine-oxazoline ligands catalyzes asym. allylic oxidn. of cyclic olefins with good conversion rates and acceptable enantioselectivity (?67% ee). The imidazolium salt I has been identified as a precursor of the N,N'-unsym. N-heterocyclic carbene ligand, which upon complexation with palladium, catalyzed the intramol. amide enolate ?-arylation leading to oxindole in excellent yield but with low enantioselectivity.

Remote chiral induction in the organocatalytic hydrosilylation of aromatic ketones and ketimines

Lewis basic, metal-free pyridyloxazolines catalyze the redn. of prochiral arom. ketones and ketimines with Cl3SiH in good enantioselectivity (? 94% ee). Arene-arene interactions between the substrate and the catalyst are likely to play a role in the enantiodifferentiation process.

Asymmetric rhodium carbene insertion into the Si-H bond: identification of new dirhodium(II) carboxylate catalysts using parallel synthesis techniques

Decomposition of methyl 2-diazophenylacetate in the presence of silanes and a chiral dirhodium(11) catalyst results in Si-H insertion of the intermediate carbenoid with varying degrees of enantioselectivity. New chiral dirhodium(11) carboxylate catalysts were identified using solution phase parallel synthesis techniques. (C) 2003 Elsevier Science Ltd. All rights reserved.

 -Hydroxypiperidinecarboxylates: additions to the chiral pool from bakers' yeast reductions of  -ketopiperidinecarboxylates.

Knight, David W.; Lewis, Neil; Share, Andrew C.; Haigh, David. Chemistry Department, University of Nottingham, Nottingham, UK. Journal of the Chemical Society, Perkin Transactions 1: Organic and Bio-Organic Chemistry (1998), (22), 3673-3684. Publisher: Royal Society of Chemistry, CODEN: JCPRB4 ISSN: 0300-922X. Journal written in English. CAN 130:153545 AN 1998:715806 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) Abstract Redn. of the piperidine keto esters, e.g., I, using fermenting bakers' yeast provides high yields of the corresponding hydroxy esters, e.g., II, exclusively as the cis-diastereoisomers and with good levels (?80%) of enantiomeric enrichment. The relative stereochemistries of the products were deduced from NMR data while the abs. configurations were detd. by degrdn. to known piperidinemethanol derivs. or, in the case of hydroxy ester III, by homologation to (R)-3-quinuclidinol IV.

New chiral rhodium(II) carboxylates and their use as catalysts in carbenoid transformations

New chiral dirhodium(II) carboxylates were prepd. from Rh2(OAc)4 and half phthalate esters and or pyrroles. Their use as catalysts for the decompn. of diazocarbonyl compds. studied.

Keratoconus: an analysis of corneal asymmetry

Background: Keratoconus, a non-inflammatory corneal ectasia, is reported to have bilateral involvement in over 90% of patients. The purpose of this study was to quantify the extent of asymmetry of disease at presentation to a regional corneal clinic.

Signatures of delayed detonation, asymmetry, and electron capture in the mid-infrared spectra of supernovae 2003hv and 2005df

We present mid-infrared (5.2-15.2 mu m) spectra of the Type Ia supernovae (SNe Ia) 2003hv and 2005df observed with the Spitzer Space Telescope. These are the first observed mid-infrared spectra of thermonuclear supernovae, and show strong emission from fine-structure lines of Ni, Co, S, and Ar. The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a SN Ia. The SN 2005df Ar lines also exhibit a two-pronged emission profile, implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co (III)], which matches the blueshift of [Fe (II)] lines in nearly coeval near-infrared spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive Ni-56 give M-56Ni approximate to 0.5 M-circle dot, for SN 2003hv, but only M-56Ni approximate to 0.13-0.22 M-circle dot for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive 56Ni yield. The observed emission-line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure, which matches the predictions of delayed detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore, the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.

Possible evidence of asymmetry in SN 2007rt, a type IIn supernova

An optical photometric and spectroscopic analysis of the slowly-evolving type IIn SN 2007rt is presented, covering a duration of 481 days after discovery. Its earliest spectrum, taken approximately 100 days after the explosion epoch, indicates the presence of a dense circumstellar medium, with which the supernova ejecta is interacting. This is supported by the slowly-evolving light curve. A notable feature in the spectrum of SN 2007rt is the presence of a broad He i 5875 line, not usually detected in type IIn supernovae. This may imply that the progenitor star has a high He/H ratio, having shed a significant portion of its hydrogen shell via mass-loss. An intermediate resolution spectrum reveals a narrow Ha P-Cygni profile, the absorption component of which has a width of 128 km s-1. This slow velocity suggests that the progenitor of SN 2007rt recently underwent mass-loss with wind speeds comparable to the lower limits of those detected in luminous blue variables. Asymmetries in the line profiles of H and He at early phases bears some resemblance to double-peaked features observed in a number of Ib/c spectra. These asymmetries may be indicative of an asymmetric or bipolar outflow or alternatively dust formation in the fast expanding ejecta. In addition, the late time spectrum, at over 240 days post-explosion, shows clear evidence for the presence of newly formed dust.

Enantioselective dioxygenase-catalysed formation and thermal racemisation of chiral thiophene sulfoxides

Substituted chiral thiophene 1-oxides and their cycloadducts of variable enantiopurity have been isolated as products of dioxygenase-catalysed sulfoxidation of the corresponding thiophenes using intact cells of Pseudomonas putida; thermal racemization (Delta G(double dagger) = 25.1 kcal mol(-1)) of the enantiopure metabolite (1R)-2-methylbenzo[b]thiophene 1-oxide has been observed.

Diastereoselective 1,3-dipolar cycloaddition of pyrylium ylides with chiral enamides

Chiral enamides5f-i were found to react with pyrylium ylides to give cycloadducts 6d-i in good yields with an excellent level of stereoselectivity. The chiral auxiliary was successfully removed on hydrogenolysis of compound 6f in continuous flow (H-Cube) resulting in the first asymmetric synthesis of complex amine 8.

The Unification of Asymmetry Signatures of Type Ia Supernovae

We present a compilation of the geometry measures acquired using optical and IR spectroscopy and optical spectropolarimetry to probe the explosion geometry of Type Ia supernovae (SNe Ia). Polarization measurements are sensitive to asymmetries in the plane of the sky, whereas line profiles in nebular phase spectra are expected to trace asymmetries perpendicular to the plane of the sky. The combination of these two measures can overcome their respective projection effects, completely probing the structures of these events. For nine normal SNe Ia, we find that the polarization of Si II ?6355 at 5 days before maximum (p Si II ) is well correlated with its velocity evolution (\dot{v}_Si II), implying that \dot{v}_Si II is predominantly due to the asymmetry of the SNe. We find only a weak correlation between the polarization of Si II and the reported velocities (v neb) for peak emission of optical Fe II and Ni II lines in nebular spectra. Our sample is biased, with polarization measurements being only available for normal SNe that subsequently exhibited positive (i.e., redshifted) v neb. In unison these indicators are consistent with an explosion in which the outer layers are dominated by a spherical oxygen layer, mixed with an asymmetric distribution of intermediate-mass elements. The combination of spectroscopic and spectropolarimetric indicators suggests a single geometric configuration for normal SNe Ia, with some of the diversity of observed properties arising from orientation effects.

Chiral supported ionic liquid phase (CSILP) catalysts for greener asymmetric hydrogenation processes

Chiral supported ionic liquid phase (CSILP) catalysts were prepared by physical adsorption (within highly porous carbons or mesoporous silica) of Ir, Ru and Rh complexes as IrCl(COD)-(S, S)-BDPP, [IrCl-(S)-BINAP](2), RuCl(p-cymene)[(S, S)-Ts-DPEN], RuOTf(p-cymene)[(S, S)-Ts-DPEN], [Rh(COD)(S, S)-DIPAMP][BF4], and [Rh(COD)(R, R)-Me-DuPHOS][BF4]. For the syntheses of CSILP catalysts [EMIM][NTf2], [BMIM][BF4] and [BMIM][PF6] ionic liquids were used. Comparative homogeneous and heterogeneous experiments were carried out using the asymmetric hydrogenation of double -C N- and -C C- bonds in trimethylindolenine, 2-methylquinoline and dimethylitaconate, respectively. The conversion and enantioselectivity was found to depend on the nature of the complex (metal and ligand), the immobilization method used, nature of the ionic liquid, nature of the support and the experimental conditions. (C) 2012 Elsevier B.V. All rights reserved.