Enantioenriched Boron C,N-Chelates via Chirality Transfer.

Molecules stereogenic only at tetrahedral boron atoms show great promise for applications, for example as chiroptical materials, but are scarcely investigated due to their synthetic challenge. Hence, this study reports a two-step synthesis of enantioenriched boron C,N-chelates. First, the diastereoselective complexation of alkyl/aryl borinates with chiral aminoalcohols furnished boron stereogenic heterocycles in up to 86 % yield and d.r. >98 : 2. Treatment of these O,N-complexes with chelate nucleophiles was surmised to transfer the stereoinformation via the ate-complex into the C,N-products. This chirality transfer succeeded by substitution of the O,N-chelates with lithiated phenyl pyridine to give boron stereogenic C,N-chelates in up to 84 % yield and e.r. up to 97 : 3. The chiral aminoalcohol ligands could be recovered after isolation of the C,N-chelates. The chirality transfer tolerated alkyl, alkynyl and (hetero-)aryl moieties at boron and could be further extended by post-modification: transformations such as catalytic hydrogenations or sequential deprotonation/electrophilic trapping were feasible while maintaining the stereochemical integrity of the C,N-chelates. Structural aspects of the boron chelates were studied by variable temperature NMR and X-ray diffraction.

Synthesis and Functionalization of Tertiary Propargylic Boronic Esters by Alkynyllithium-Mediated 1,2-Metalate Rearrangement of Borylated Cyclopropanes.

Implementing the use of alkynyllithium reagents in a stereospecific 1,2-metalate rearrangement-mediated ring opening of polysubstituted cyclopropyl boronic esters provides a variety of tertiary pinacol boranes bearing adjacent tertiary or quaternary carbon stereocenters with high levels of diastereomeric purity. The potential of this strategy was demonstrated through a selection of α- and γ-functionalization of the propargyl boronic esters.

Synthesis of Highly Functionalized Hydrindanes via Sequential Organocatalytic Michael/Mukaiyama Aldol Addition and Telescoped Hydrozirconation/Cross-Coupling as Key Steps: En Route to the AB System of Clifednamides.

The AB ring systems of the clifednamide family, polycyclic tetramate macrolactames (PoTeMs), were prepared by a new, convergent approach employing an intramolecular Diels-Alder (IMDA) reaction. Key steps comprise an organocatalytic Michael addition (>90% enantiomeric excess (ee)), a Mukaiyama aldol reaction for the convergent installation of a diene moiety, and a telescoped hydrozirconation/cross-coupling grafting an enone. The following IMDA furnished a highly functionalized hydrindane (diastereomeric ratio (dr) = 91:1) with the same configuration as the clifednamide scaffold. Advantages of this route are only one required protecting group, 13% overall yield over 9 steps (reduced from previously 17 steps/1.3% overall), and the potential access to the key intermediates in the clifednamide biosynthesis.

Fluorophobic Effect Promoting Lamellar Self-Assembly of Donor Acceptor Dyes.

To combine liquid crystalline and linear optical properties in the same molecule, the fluorophobic effect was probed for the first time in donor acceptor dyes. Thus, a series of mono-, bi-, and tricyclic donor acceptor dyes with 1H,1H-perfluorinated alkyl chains of different lengths as donor units and nitrile, malononitrile or barbiturate as acceptor units was synthesized in 5 steps and 1.4-6.6 % overall yield. UV/Vis and fluorescence spectroscopy, cyclic voltammetry and DFT calculations revealed that absorption and emission maxima, Stokes shifts and LUMO energies were mainly governed by the chromophore size and acceptor strengths. The perfluorinated chain was electronically almost decoupled from the remaining chromophore and induced only slight changes of the absorption maxima as compared to the alkyl substituted counterparts. However, in contrast to the non-mesomorphic alkyl donor-substituted derivatives, the perfluorinated donors resulted in self-assembly into partially interdigitated SmA bilayers according to differential scanning calorimetry (DSC), polarizing optical microscopy (POM), X-ray diffraction (WAXS, SAXS) studies and electron density profile calculations.

Large Electro-Optic Kerr Effect in Ionic Liquid Crystals: Connecting Features of Liquid Crystals and Polyelectrolytes.

The electro-optic Kerr effect in simple dipolar fluids such as nitrobenzene has been widely applied in electro-optical phase modulators and light shutters. In 2005, the discovery of the large Kerr effect in liquid-crystalline blue phases (Y. Hisakado et al., Adv. Mater. 2005, 17, 96-98.) gave new directions to the search for advanced Kerr effect materials. Even though the Kerr effect is present in all transparent and optically isotropic media, it is well known that the effect can be anomalously large in complex fluids, namely in the isotropic phase of liquid crystals or in polyelectrolyte solutions. Herein, it is shown that the Kerr effect in the isotropic phase of ionic liquid crystals combines the effective counterion polarization mechanism found in polyelectrolytes and the unique pretransitional growth of the Kerr constant found in the isotropic phase of nematic liquid crystals. Maximum Kerr constants in the order of several 10-11  m V-2 (ten times higher than the Kerr constant of the toxic nitrobenzene and less temperature sensitive than Kerr constants of nematic liquid crystals) make ionic liquid crystals attractive as new class of functional materials in low-speed Kerr effect applications.

Deoxycyanamidation of Alcohols with N-Cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS).

The first one-pot deoxycyanamidation of alcohols has been developed using N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) as both a sulfonyl transfer reagent and a cyanamide source, accessing a diverse range of tertiary cyanamides in excellent isolated yields. This approach exploits the underdeveloped desulfonylative (N-S bond cleavage) reactivity pathway of NCTS, which is more commonly employed for electrophilic C- and N-cyanation processes.