Although discotic liquid crystals are attractive functional materials, their use in electronic devices is often restricted by high melting and clearing points. Among the promising candidates for applications are [15]crown-5 ether-based liquid crystals with peripheral n-alkoxy side chains, which, however, still have melting points above room temperature. To overcome this problem, a series of o-terphenyl and triphenylene [15]crown-5 ether derivatives was prepared in which δ-methyl-branched alkoxy side chains of varying lengths substitute the peripheral linear alkoxy chains. The mesomorphic properties of the novel crown ethers were studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. δ-Methyl branching indeed lowers melting points resulting in room-temperature hexagonal columnar mesophases. The mesophase widths, which ranged from 87 to 30 K for o-terphenyls, significantly increased to 106-147 K for the triphenylenes depending on the chain lengths, revealing the beneficial effect of a flat mesogen, due to improved π-π interactions.
The Ni(NHC) catalyzed rearrangement of 1‐acyl‐2‐vinylcyclopropanes to the corresponding 4‐acyl‐cyclopent‐1‐enes is highly promising for the synthesis of keto‐functionalized annelated bi‐ and tricyclic subunits of natural products. Therefore, we investigated the catalytic activity of Ni(NHC) complexes in the rearrangement of 1‐acyl‐2‐vinylcyclopropanes with different ring sizes and substitution patterns. Surprising effects regarding substrate scope and stereoselectivity of the Ni(NHC) catalyzed vinylcyclopropane‐cyclopentene rearrangement were observed. Only vinylcyclopropanes with 1‐methyl, 1‐phenyl, 1,2‐dialkyl or 2‐phenyl‐substitution at the vinyl moiety could be rearranged successfully. Moreover, an endo‐configuration on the cyclopropane ring was required for successful rearrangement. By treatment of the vinylcyclopropanes with Rh catalysts or Lewis acids, the involvement of Lewis acid catalysis could be ruled out. In order to understand these experimental results and to rationalize the reactivity of the Ni(NHC) complexes computational studies were performed, which provided insights into mechanistic details.
The synthesis of a range of racemic 1-acyl-2-vinylcyclopropanes by using two different methodologies is studied. We have developed a copper-catalyzed process for converting diazoketones into 1-acyl-2-vinylcyclopropanes and a sulfur-ylide-mediated procedure which allows, in only two steps, a simplified access to 1-acyl-2-vinylcyclopropanes with alkyl or aryl substituents on the alkene moiety.
The reaction of 2-chloro-6,7-dimethoxy-3-nitroquinoline with a series of amines and aminoalkanoates under basic microwave-mediated conditions and under Buchwald–Hartwig amination conditions is reported. The microwave irradiation favored the reaction with amines, resulting in yields of up to 80%, whereas amino acid functionalization gave yields comparable to those of Buchwald–Hartwig amination. tert-Butyl (2R)-4-[(6,7-dimethoxy-3-nitroquinolin-2-yl)amino]-2-hydroxybutanoate was successfully cyclized to the pyoverdin chromophore, a subunit of siderophores.
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