Copper-Catalyzed Enantioselective Reductive Aldol Reaction of α,β-Unsaturated Carboxylic Acids to Alkyl Aryl Ketones: Silanes as Activator and Transient Protecting Group

The first enantioselective reductive aldol reaction of unprotected α,β-unsaturated carboxylic acids was developed by employing a copper/bisphosphine catalyst. The reaction features in situ protection and activation of an α,β-unsaturated carboxylic acid by a hydrosilane. The copper enolate formed in situ reacts with an alkyl aryl ketone to afford the β-hydroxy carboxylic acid with excellent enantioselectivity (up to 99 % ee). The corresponding gram-scale reaction with a low catalyst loading and the derivatization of the β-hydroxy carboxylic acids highlight the practicality of this transformation.     

Molecular Packing and Solid-State Photophysical Properties of 1,3,6,8-Tetraalkylpyrenes

The relationship between the photophysical properties and molecular orientation of 1,3,6,8-tetraalkylpyrenes in the solid state is described herein. The introduction of alkyl groups with different chain structures (in terms of length and branching) did not affect the photophysical properties in solution, but significantly shifted the emission wavelengths and fluorescence quantum yields in the solid state for some samples. Pyrenes bearing ethyl, isobutyl, or neopentyl groups at the 1-, 3-, 6-, and 8-positions showed similar emission profiles in both the solution and solid states. In contrast, pyrenes bearing other alkyl groups exhibited an excimer emission in the solid state, similar to that of the parent pyrene. On studying the photophysical properties in the solid state with respect to the obtained crystal structures, the observed solid-state photophysical properties were found to depend on the relative position of the pyrene chromophores. The solid-state photophysical properties can be controlled by the alkyl groups, which provide changing crystal packing. Among the pyrenes tested, 1,3,6,8-tetraethylpyrene showed the highest fluorescence quantum yield of 0.88 in the solid state.     

Near-Infrared Electrochromic Behavior of Dibenzothiepin Derivatives Attached with Two Michler's Hydrol Blue Units

10,11-Bis[bis(4-dimethylaminophenyl)methylene]dibenzo[bf]thiepin ( 1 ) and -oxepin ( 2 ) were prepared as stable yellow crystalline compounds, which are the cyclic analogues of electron-donating hexaarylbutadienes. Upon two-electron oxidation, they are reversibly transformed into the title dications ( 1 ²⁺ and 2 ²⁺) exhibiting near-infrared (NIR) absorptions, which were also isolated as stable salts. These redox pairs can serve as new entries into less well-explored organic NIR-electrochromic systems, and the separation of redox peaks (electrochemical bistability) was attained for 1 / 1 ²⁺ and 2 / 2 ²⁺, thanks to drastic geometrical changes between neutral and dicationic states, as revealed by a series of X-ray analyses. Thiepin-S,S-dioxide analogue ( 3 / 3 ²⁺) exhibits quite similar dynamic redox behavior due to nonaromatic nature of the dibenzothiepin and -oxepin unit in 1 ²⁺ and 2 ²⁺, whereas the thiepin-S-oxide derivative ( 4 / 4 ²⁺) does not exhibit bistability due to the smaller change in geometry upon electron transfer, showing that a subtle change of a bridging atom in the central seven-membered ring can modify the redox properties.     

Increasing useful magnification in ocular systems

The magnifying power of ocular systems is limited by the system exit pupil and Lagrange Invariant. This work shows that useful magnification is increased by separating the invariant. The impact on the specification for digital ocular systems, including a binocular example, is provided.     

Tandem five membered-ring selective Prins reaction and Friedel–Crafts reaction

A tandem reaction consisting of five membered-ring selective Prins cyclization and subsequent Friedel–Crafts cyclization was developed. The reactions of phenyl homoallylic alcohol 3 and benzaldehyde derivatives 6 afforded tetrahydroindenofurans 7 or pentacyclic products 8, depending upon the quantity of 6. Also homoallylic alcohol 12 having an alkyne–cobalt moiety reacted with 6 to give rise to tetrahydroindenofurans 13 in good yields.     

Controllability of dynamic double helices: quantitative analysis of the inversion of a screw-sense preference upon complexation

We describe a quantitative analysis of the complexation-induced inversion of a screw-sense preference based on a conformationally dynamic double-helix structure in a macrocycle. The macrocycle is composed of two twisting units (terephthalamide), which are spaced by two strands (1,3-bis(phenylethynyl)benzene), and is designed to generate a double-helix structure through twisting about a C₂ axis in a conrotatory manner. The attachment of chiral auxiliaries to the twisting units induces a helical preference for a particular sense of (M)- or (P)-helicity through the intramolecular transmission of chirality to dynamic double helices. The twisting unit can also act as a binding site for capturing a guest molecule, and, in a complexed state, the preferred screw sense of the dynamic double-helix structure is reversed to exhibit the contrary preference. We quantitatively monitored the complexation-induced inversion of the screw-sense preference using ¹H NMR spectroscopy, which enabled us to observe independently two species with (M)- or (P)-helicity in both the absence and presence of a guest molecule. Inversion of the screw-sense preference was induced upon complexation with an achiral guest as well as a chiral guest.     

Enantio‐ and Stereoselective Cyclopolymerization of Hexa‐1,5‐diene Catalyzed by Zirconium Complexes Possessing Optically Active Bis(phenolato) Ligands

Enantio‐ and stereoselective cyclopolymerization of hexa‐1,5‐diene was achieved by enantiomerically pure dichloro zirconium(IV) pre‐catalysts 2 possessing chiral [OSSO]‐type bis(phenolate) ligands (−)‐ 1 and (+)‐ 1 in combination with dried methylaluminoxane (dMAO) as an activator. The corresponding activities were recorded with quite high values up to 1,960 g mmol( 2 )^–1 h^–1, which are extremely larger than those of the related complexes. The microstructure analysis for the PMCPs furnished by pre‐catalysts (Λ,S,S)‐ 2 and (Δ,R,R)‐ 2 showed good isotacticity factors (α = 75−78%) and relatively high proportions of trans‐cyclopentane rings (σ = 14−21%). These enantiomeric PMCPs exhibited large specific optical rotations ([α]_D = +28 to +32° from (Λ,S,S)‐ 2 , −26 to −34° from (Δ,R,R)‐ 2 ).

     

Use of silk protein, sericin, as a sustained-release material in the form of a gel, sponge and film

To evaluate the usability of silk protein (sericin, SC) as a sustained-release material, the physicochemical properties of SC and the release profiles of model drugs from SC gel, sponge and film were studied. Heat aids the dissolution of SC. The molecular weight of SC tended to decrease as the heating temperature and heating time increased. The gel and sponge formed by SC were moldable and consisted of high molecular weight SC polymers (250 kDa and about 400 kDa). SC film was easily broken and exhibited elastic distortion. The addition of moisture-retaining plasticizer (glycerin and sorbitol) improved the film-forming characteristics of SC. The results suggested that SC is practical as a moldable gel and sponge, and as a tensible film. To evaluate the release profiles of small molecules, fluorescein isothiocyanate-dextran ((1) FD4, 4 kDa and (2) FD70, 70 kDa) were used as two model drugs with significantly different molecular weights, and fluorescein isothiocyanate-albumin ((3) FA, 66 kDa) was used as a charged drug. Each was formulated in SC gel, sponge and film. In each preparation, the release rate of the model drugs tended to be FA相似文献