Ir-catalyzed asymmetric allylic alkylation using chiral diaminophosphine oxides: DIAPHOXs. Formal enantioselective synthesis of (−)-paroxetine

An Ir-catalyzed asymmetric allylic alkylation using chiral diaminophosphine oxide is described. Asymmetric allylic alkylation of terminal allylic carbonates proceeded using 5 mol % of Ir catalyst, 5 mol % of DIAPHOX 1i, 10 mol % of NaPF₆, 10 mol % of LiOAc, and N,O-bis(trimethylsilyl)acetamide (BSA), affording the corresponding branched products in excellent yield and in up to 95% ee. The developed catalytic asymmetric reaction was successfully applied to a formal enantioselective synthesis of (−)-paroxetine.     

Ab initio molecular orbital study of ground and low-lying electronic states of CoCN

The ground and low-lying excited states of CoCN have been studied by ab initio multireference single and double excitation configuration interaction (MR-SDCI) calculations with Davidson's correction Q and Cowan-Griffin's relativistic corrections. The electronic ground state of CoCN is (3)Phi(i) and the equilibrium geometry is linear with bond lengths of r(e)(Co-C)=1.8540 A and r(e)(C-N)=1.1677 A, substantially different from the experimentally derived values of r(0)(Co-C)=1.8827(7) A and r(0)(C-N)=1.1313(10) A. The first excited state is (3)Delta(i), separated from the ground state by 727 cm(-1). Larger dynamical electron correlation energy for the low-spin (3)Phi state than for the high-spin (5)Phi state makes the (3)Phi state to be the ground state, which is discussed in terms of the differences in natural orbitals. A new spin-orbit interaction scheme between the X (3)Phi(i) and 1 (3)Delta(i) states is proposed.     

Diffusion in a sol-gel-derived medium with a view toward biosensor applications

Time-resolved fluorescence anisotropy and fluorescence recovery after photobleaching were applied to study the diffusion of dyes and a fluorescence-labeled enzyme in a sol-gel-derived medium. This type of medium exhibits attractive properties such as robustness, low processing temperature, high porosity, large internal surface area, and can act as protective immobilization media for biologically active molecules. This makes it a suitable candidate for biosensor applications. The glasslike nature and good optical quality allows for light addressable entities to be incorporated and accessed using spectroscopy. This type of matrix, once formed, can be anything from an ordered gel to a robust glassy block depending on the aging process. In this work we apply confocal microscopy and time-resolved fluorescence techniques to study both rotational and lateral diffusion with aging time within a silica sol-gel derived monolith. An enzyme, horseradish peroxidase, was labeled with Alexa Fluor 488 and rotation related to both the enzyme and the probe monitored during the matrix aging process. Diffusion coefficients of between ca. 0.5 x 10(-7) and 4 x 10(-7) cm2 s(-1) were obtained from preliminary FRAP measurements of fluorescein and correlated to differences in the catalytic activity of HRP incorporated in the monolith.     

Highly stereoselective construction of 4,6-cis-substituted quinolizidine ring core: an application to enantioselective total synthesis of the marine alkaloid clavepictines A, B and pictamine

The enantioselective total synthesis of the marine alkaloids clavepictines A, B and pictamine has been achieved through the highly stereocontrolled quinolizidine ring closure of the conformationally constrained piperidine ring system (2), which bears the chiral centers and appropriate functionality needed for the synthesis of target alkaloids. The absolute stereochemistry of clavepictines and pictamine was verified to be 3R, 4S, 6S, 9aS by the present synthesis.     

Cyclic carbonates,novel expandable monomers on polymerization

A variety of cyclic carbonates was shown to undergo volume expansion on polymerization. The degree of volume expansion, which was measured by the density gradient tube method, was ranging from 1.1% to 7.7%. The volume expansion was examined by assuming a change in molecular interaction such as dipole moment between monomer and polymer states.     

First application of the depth profile of silica species as a tracer by fast‐atom bombardment mass spectrometry: investigation of the circulation of seawater and silica uptake by diatoms

Silica, represented by SiO₂, is the general name for the compounds composed of Si, O and H with their derivative complexes. Silica forms various chemical species in aquatic solutions, such as a monomer (Si(OH)₃O⁻), dimer (Si₂(OH)₅O), and others. These species are known to vary in their relative abundances in solution depending on the chemical and physical conditions. Silica species dissolved in seawater have been examined by fast-atom bombardment mass spectrometry (FAB-MS) to elucidate the behavior of silica and its circulation as a novel tracer reflecting the chemical and physical conditions of seawater and the bioactivity of diatoms, which take up silica. In the seawater of Tokyo Bay, silica species such as [Si(OH)₂O₂Na]⁻ ([monomer–Na]⁻), [Si₂(OH)₅O₂]⁻ ([dimer]⁻), [Si₂(OH)₄O₃Na]⁻ ([dimer–Na]⁻), [Si₄(OH)₇O₅]⁻ ([cyclic tetramer]⁻), [Si₄(OH)₆O₆Na]⁻ ([cyclic tetramer–Na]⁻), [Si₄(OH)₉O₄]⁻ ([linear tetramer]⁻) and [Si₄(OH)₈O₅Na]⁻ ([linear tetramer–Na]⁻) were observed and assigned by FAB-MS. To investigate the suitability of silica species as a tracer, the relative peak intensity ratios of silica species observed in the mass spectra, i.e. the profiles of the ratio of the linear tetramer to the cyclic tetramer (m/z 329/311) and the ratio of the dimer to the cyclic tetramer (m/z 173/311) against depth, were examined to determine the annual changes and reproducibility of the depth profiles. In particular, the depth profile of the relative ratio of the linear tetramer to the cyclic tetramer, 329/311, exhibits critical changes depending on the seawater budget. These changes in the relative ratios were identified by an experiment involving a simple sodium chloride solution system. Our measurement is expected to elucidate the dynamics of silica and its role as ‘food’ for diatoms, and we showed that speciation using mass spectrometry is a powerful tool for examining elemental behavior in nature and environmental changes. Our results suggest that a silica tracer is useful for investigating the behavior of seawater in small coastal regions and the uptake of silica by diatoms. Copyright © 2009 John Wiley & Sons, Ltd.     

Hypervalent Iodine(III) Sulfonate Mediated Synthesis of Quinoxalines in Liquid PEG‐400

PEG‐400[poly(ethylene glycol‐400)] is used as a “green” recyclable solvent in the one‐pot synthesis of quinoxalines by reaction with aryl ketones, hypervalent Iodine(III) Sulfonate, and o‐phenylenediamines. Significant rate enhancements and improved yields have been observed.     

On the Function and Structure of Synthetically Modified Porins

The attachment of modulators to a trimeric porin ion channel was investigated (see picture of the trimer with a crown ether modulator (orange)). The interplay of modulator and protein is essential for the conformational heterogeneity of the hybrid channel. Single‐site attachment in large pores is not sufficient to change the electrophysiological characteristics of the pores—such change requires additional noncovalent interactions or second‐site attachments.

     

Accelerated electrocyclic ring-opening of benzocyclobutenes under the influence of a beta-silicon atom

A significant acceleration effect of a beta-silicon atom was observed on the electrocyclic ring-opening reaction of benzocyclobutene derivatives to form o-quinodimethanes. This acceleration effect could be attributed to an electronic sigma-donating nature of the C(alpha)-Si(beta) bond, associated with alpha-anion driven pericyclic reactions.     

In situ generation of 3,3,3-trifluoropropanal and its use for carbon-carbon bond-forming reactions

The DIBAL reduction of 2-phenylethyl 3,3,3-trifluoro-2-methylpropionate 2 at -78 degrees C afforded the aluminum acetal 3, and this intermediate, on worming up to 0 degrees C, was found to slowly decompose into the corresponding aldehyde 4, which smoothly reacted with appropriate nucleophiles in a one-pot manner in good to excellent yields with up to 93% diastereoselectivity.