A convenient and stereoselective synthesis of 11Z-3,4-didehydroretinal by Horner-Emmons reaction using diphenyl phosphonate

A convenient synthesis of 3,4-didehydroretinal was developed. The Horner-Emmons reaction between 3,4-didehydro-beta-ionone and diphenyl phosphonate in the presence of crown ether gave the retinonitrile as an isomeric mixture, in which the newly produced double bond was predominantly 11Z-form. After separation of the 11Z-form retinonitrile, it was converted into the corresponding retinal in good yield without isomerization of the double bonds.     

Novel chiral cyclic polysulfides with a biphenyl backbone: investigation of atropisomerism and pentathiepin ring inversion

Novel axially chiral benzopolysulfides were synthesized on biaryls by sulfurization of dithiastannoles. Pentathiepin, trithiole, and trithiole 2-oxide rings were observed as single isomer on 1,1′-biaryls. The rotational energy barrier of chiral axis was increased by incorporation of a methyl group at ortho-position. In that case, both trithiole oxide and pentathiepin rings appeared as diastereomer. ortho-Tolyl functionality was also replaced by naphthyl moiety to create more rotational hindrance. Chiral axis was incorporated at the neighborhood of polysulfide functionality by Suzuki-Miyaura cross-coupling reaction. Calculated rotational energy barriers were very much consistent with experimental observations to show atropisomerism. Energy barrier for the inversion of pentathiepin ring was experimentally determined by variable temperature ¹H NMR. The kinetic data suggested that pentathiepin ring inversion was prompt in solution. Insufficient rotational energy barriers of chiral axis and pentathiepin ring inversion make substantially impossible to separate optically pure diastereomer even by chiral chromatography [Preliminary report: Sato, R.; Ohta, H.; Yamamoto T.; Nakajo, S.; Ogawa, S.; Alam, A. Tetrahedron Lett.2007, 48, 4991-4994.].     

Co‐syndiospecific Alternating Copolymerization of Functionalized Propylenes and Styrene by Rare‐Earth Catalysts

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co‐syndiospecific alternating copolymerization of methoxyphenyl‐ and N,N‐dimethylaminophenyl‐functionalized propylenes with styrene by half‐sandwich rare‐earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene‐alt‐styrene copolymers with a perfect alternating sequence and excellent co‐syndiotacticity (rrrr >99 %), thus constituting the first example of co‐stereospecific alternating copolymerization of polar and non‐polar olefins.     

Synthesis of an Alternated Heterobimetallic Supramolecular Polymer Based on Ru(II) and Fe(II)

A heterobimetallic supramolecular polymer (polyRuFe) with alternately complexed Ru(II) and Fe(II) is prepared following a stepwise synthetic route through harnessing first the strongly binding metal ion Ru(II) and then the weakly binding metal ion Fe(II). A high yield of product is achieved in each step. The heterometal ions are incorporated into the polymer chain in identical coordination environments formed by two 2,2′:6′,2″-terpyridine moieties. Characterization is accomplished by NMR spectroscopy, MALDI–TOF mass spectrometry, UV–Vis spectroscopy, and cyclic voltammetry. PolyRuFe shows a wide optical window (λ = 311–577 nm) and a broad distinct reversible redox nature of two types, originated from the coupling of the two heterometallic segments into the polymer chain. Such characteristics of polyRuFe suggest its potential for various electrochemical and electro-optical applications.     

THE CONFORMATIONAL ANALYSIS AND PHOTOISOMERIZATION OF RETINOCHROME ANALOGS WITH POLYENALS

Abstract— 3, 7-Dimethyl-2, 4, 6, 8, 10-dodecapentaenal was synthesized for reconstitution of the retinochrome analog. Its opsin shift was 1000 cm ¹ smaller than that of native retinochrome, whose chromophore contains the same number of double bonds. The conformational change from 6-s-trans to 6-s-cis , as figured in a retinal molecule, plays an important role in the formation of the retinochrome analog, based on the estimation of opsin shifts for retinal analogs locked in the 6-s conformation. Thus the conformation of the 6–7 single bond in the native retinochrome was suggested to be 6 -cis . Analysis of the circular dichroic spectra of retinochrome analogs revealed that the 6-s conformation is independent of the appearance of the β-band. The stereoselectivity in the photoisomerization of the retinal analogs by a retinochrome template depends on the hydrophobic binding in the region of the β-ionone ring.     

Lithium secondary batteries using modified-imidazolium room-temperature ionic liquid

Highly reversible, safe lithium secondary batteries that use imidazolium-cation-based room-temperature ionic liquid as an electrolyte and lithium metal as an anode material were realized by the molecular design. To achieve higher reduction stability, an electron-donating substituent was introduced to promote charge delocalization in the imidazolium cation of room-temperature ionic liquids.     

Asymmetric synthesis of α,α-disubstituted α-amino alcohol derivatives

Herein we report the asymmetric synthesis of α,α-disubstituted α-amino alcohol derivatives 22, 25 and 26, key intermediates of a novel immunomodulator, using Seebach’s method. This synthetic method can be applied to the large scale synthesis of chiral sphingosine 1-phosphate-1 (S1P₁) receptor agonists, with significant improvements to the previously reported method with regard to the reaction temperature.     

Third-order nonlinear optical properties of open-shell supermolecular systems composed of acetylene linked phenalenyl radicals

The third-order nonlinear optical (NLO) properties, at the molecular level, the static second hyperpolarizabilities, γ, of supermolecular systems composed of phenalenyl and pyrene rings linked by acetylene units are investigated by employing the long-range corrected spin-unrestricted density functional theory, LC-UBLYP, method. The phenalenyl based superethylene, superallyl, and superbutadiene in their lowest spin states have intermediate diradical characters and exhibit larger γ values than the closed-shell pyrene based superpolyene systems. The introduction of a positive charge into the phenalenyl based superallyl radical changes the sign of γ and enhances its amplitude by a factor of 35. Although such sign inversion is also observed in the allyl radical and cation systems in their ground state equilibrium geometries, the relative amplitude of γ is much different, that is, |γ(regular allyl cation)/γ(regular allyl radical)| = 0.61 versus |γ(phenalenyl based superallyl cation)/γ(phenalenyl based superallyl radical)| = 35. In contrast, the model ethylene, allyl radical/cation, and butadiene systems with stretched carbon-carbon bond lengths (2.0 ?), having intermediate diradical characters, exhibit similar γ features to those of the phenalenyl based superpolyene systems. This exemplifies that the size dependence of γ as well as its sign change by introducing a positive charge on the phenalenyl based superpolyene systems originate from their intermediate diradical characters. In addition, the change from the lowest to the highest π-electron spin states significantly reduces the γ amplitudes of the neutral phenalenyl based superpolyene systems. For phenalenyl based superallyl cation, the sign inversion of γ (from negative to positive) is observed upon switching between the singlet and triplet states, which is predicted to be associated with a modification of the balance between the positive and negative contributions to γ. The present study paves the way toward designing a variety of open-shell NLO supermolecular systems composed of phenalenyl radical building blocks.     

Synthesis of thiophene-capped [2]rotaxanes

Two types of thiophene-capped [2]rotaxanes, i.e., bithienyl (2T)- and bis(3,4-ethylenedioxythiophene)-yl (BEDOT)-capped [2]rotaxanes, were synthesized. The electron-deficient cyclophane of cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) was used as a macrocycle. Association constants for inclusion complexation of 2T- and BEDOT-derivatives with CBPQT⁴⁺ were obtained by ¹H NMR titration. Due to the donor-acceptor charge transfer absorption band, 2T- and BEDOT-capped [2]rotaxanes have red and green colors, respectively. On the basis of electrochemical analysis, we confirmed that only BEDOT-capped [2]rotaxane is a promising candidate for [3]rotaxane synthesis through oxidation coupling of the thiophene unit.