No abstract

The (dl) a-keto esters 16, were prepared from the (dl) carbinols 1 to and from (dl) -2-hydroxyheptaElicene 5. These (dl) a-keto esters underwent NaBHq reductions to give the corresponding diastereomeric (dl) a-hydroxy esters 11, with 54 to -100% diastereaneric excesses.Highly enantioselective and/or diastereoselective syntheses are of great importance in organic chemistry. As an ultimate goal we aimed at the preparation and use o f chiral secondary alcohols and phenolewhich could lead to highly effective asymmetric inductions.process to evaluate the steric approach control as it is easy to modulate the bulkyness of the alkoxy moety of the ester '.available2'3 and proved to be efficient inducers in the reduction of the corresponding a-keto esters with NaBH4.The NaBH' reduction of a-keto esters was considered to be an efficient We have studied four secondary (dl) alcohols (1 to i) which are readily

Sonogashira coupling of dibromo- and diethynyl-substituted benzenes and fluorenes in aqueous mini-emulsion afforded colloidally stable dispersions of highly fluorescent 60-120 nm particles of poly(arylene ethynylene)s of molecular weights M(n) 4 × 10(4)-2 × 10(5) g mol(-1) with solids contents up to 15 wt %. By covalent incorporation of diethynyl pyrrolo-pyrrole or diethynyl fluorenone in the mini-emulsion polymerization the emission color of these photostable nanoparticles can be tuned from blue (λ(em max) 470) to orange at a given excitation wavelength due to an efficient energy transfer to these acceptors. Two-photon action cross sections of the particles amount to 10(6) to 10(7) GM. The particles from emulsion polymerization are taken up by HeLa cells without an adverse effect on the cells. Differentiation of the location in cells of particle species varying in emission color was demonstrated for both linear and two-photon excitation microscopy in the NIR regime.

Materials and General Considerations. Unless noted otherwise, all manipulations of ruthenium complexes were carried out under an inert atmosphere using standard glovebox or Schlenk techniques. Toluene was distilled from sodium under argon. Demineralised water was distilled under nitrogen and degassed three times after distillation. Ruthenium alkylidenes 2 and 3 were supplied by Aldrich. NMR spectra were recorded on a Varian Unity INOVA 400 or on a Bruker AC 250 spectrometer.1 H and 13C NMR chemical shifts were referred to the solvent signal. Dynamic light scattering was carried out on a Malvern Nano-ZS ZEN 3600 particle sizer (173° back scattering). The autocorrelation function was analyzed using the Malvern dispersion technology software 3.30 algorithm to obtain volume and number weighted particle size distributions. For the determination of particle size, a few drops of a latex sample were diluted with ca. 3 mL of water. TEM images were obtained on a Zeiss Libra 120 instrument (acceleration voltage 120 keV). Dispersions were dialyzed for TEM analysis to remove any free surfactant, and applied to a copper grid. Samples were not contrasted. Absorption spectra were recorded on a Varian Cary 50 spectrometer. Fluorescence spectra were obtained on a tailor-made setup consisting of a xenon flash lamp, a monochromator (Oriel 77250 1/8M), a spectrograph and a nitrogen-cooled CCD camera enabling photoluminescence detection from 310 nm to 940 nm.1 Excitation wavelengths were chosen according to the respective absorption maxima. Synthesis of Monomer 1.2-4 1,4-Dipropoxybenzene. KOH (81 g, 1.44 mol) was added to a solution of hydroquinone (64.2 g, 0.58 mol) in dry ethanol (550 mL), and refluxed for 20 minutes with mechanical stirring. 1-Bromopropane (200 mL, 2.2 mol) was added dropwise over the course of 1 hour, and the mixture was refluxed for another 3 hours. After solvent evaporation in vacuo, the residue was extracted with 500 mL CHCl 3 . The organic phase was filtered, extracted three times with 200 mL water, washed with 250 mL saturated NaHCO 3 solution, and dried over Na 2 SO 4 . Solvent evaporation yielded the crude product, which was recrystallized three times from methanol (50 mL), to afford 85 g (75% yield) of white crystals. 1 H NMR (CDCl 3 ,δ): 6.81 (4H, s), 3.86 (4H, t), 1.76 (4H, sextet), 1.01 (6H, t) 1,4-Diiodo-2,5-dipropoxybenzene. ICl (175 g, 1.08 mol) was added dropwise to 300 mL of methanol, keeping the temperature below 10°C. After slow addition of 1,4-dipropoxybenzene (48.5 g, 0.25 mol) at 10°C, the mixture was refluxed for 4h. Cooling to room temperature and standing over night afforded needle-like crystals, which were collected by filtration. The crystals were rinsed three times with 100 mL of cold methanol, and recrystallized from methanol to afford 49.1 g (44% yield) of white product. 1 H NMR (CDCl 3 , δ): 7.17 (2H, s), 3.89 (4H, t), 1.83 (4H, sextet), 1.06 (6H, t)Konstanzer Online-Publikations-System (KOPS)

SUMMARYAtrolactic syntheses have been carried out to evaluate the potentiality, in asymmetric syntheses, of chiral inducers. The (d1)-hydroxyhelicenes l, 2, the (dl) sec. alcohols 1-12 and the (d1)phenolic binaphtyl compound have been used as inducers. The d.e. are collected in table I (6-100%). The atrolactic asymmetric synthesis has also been carried out using three optically active inducers, namely : (-)-quinine 13, (-)-l0,ll-dihydroquinine -14, and R(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol 5. Diastereomeric and enantiomeric excesses equal or greater than 88% have been obtained in six cases out of sixteen :(l-naphtyl)-(9-anthryl)methanol 3 (d.e = 90%) ; 2,2,2-trichloro-1-(9-anthryl) ethanol 7 (d.e = 100% ?2), 2,2,2-tribromo-1-(9-anthryl)ethanol 8 (d.e = 100% +2), (-)=quinine 13 (e.e = 95.5%), and (-)-2,2,2-trifluoro-l-(9-anthryl) ethanol 6 (e.e = 88%).