Synthesis and Mesomorphic Properties of Novel Dibenz[a,c]anthracenedicarboximides

Unusual Photochemistry in Aromatic Dithioimides: Quantitative Thione Reduction Promoted by Ether Solvents

We report a mechanistic investigation of an aromatic dithioimide (2SS) displaying puzzling yet efficient photochemistry in ether solvents. Perplexingly, 2SS dissolved in ether solvents in a sealed and degassed vial was photochemically converted to the corresponding diimide (2OO), as determined by 1H NMR following product extraction. With no external sources of oxygen in the sample, could the oxygen in 2OO be from the ether itself? To study this unprecedented proposition, we attempt to uncover the ether's involvement in this reaction. As seen by laser-flash photolysis, 2SS appears to first react with the solvent from its singlet excited state. Following the reaction by NMR under rigorously oxygen- and water-free conditions led to the identification of a photoreductive pathway that quantitatively transformed one thione into a methylene to yield 2SH2. Subsequent oxidation of 2SH2 or irradiation of 2SS under air proved that molecular oxygen was indeed necessary to observe an oxidative pathway leading to 2OO, ruling out the initially proposed involvement of an ether oxygen. An explanation of 2SS desulfurization was further revealed through the study of solvent by-products by GC-MS analysis. Supported by DFT calculations, a mechanism is proposed to involve a chain reaction initiated by photochemically generated ether radical.

Temperature-Controlled Divergent Hydroamination Cyclization [2+2]-Cycloaddition Cascade Reactions of Homopropargylic Amines with 2-Butynedioates: Direct Access To Pyrrolo- b-cyclobutene and Dihydro-1 H-azepines

The diversified temperature-controlled hydroamination cyclization cascade reactions of homopropargylic amines and 2-butynedioates were developed for the construction of various pyrrolo- b-cyclobutenes and dihydro-1 H-azepines, respectively. This reaction actually involved an intramolecular hydroamination cyclization of homopropargylic amines to give the active dihydropyrroles intermediates, which subsequently underwent [2+2]-cycloaddition with 2-butynedioates to generate the pyrrolo- b-cyclobutenes at no more than 120 °C. Alternatively, the dihydro-1 H-azepines were directly produced at 150 °C in the reactions of homopropargylic amines and 2-butynedioates. The application of substrate scope was wide, and the corresponding products were obtained in high to excellent yields.

The impact of molecular symmetry and shape on the stability of discotic liquid crystals

Three series of dibenzo[a,c]phenazines were prepared in an order to assess the impact of side chain position on the phase stability of columnar liquid crystals. Each series was composed of four isomeric compounds differing only in the disposition of hexyloxy and decyloxy chains around the central aromatic core, giving rise to electronically similar compounds with varying shapes and symmetries. The substitution pattern was found to have a moderate effect on the clearing transition of the liquid crystal but a larger impact on the melting temperatures. These observations suggest a viable strategy for controlling the phase range of liquid crystals via judicious choice of peripheral chain structure and location.

Probing the structural features that influence the mesomorphic properties of substituted dibenz[a,c]anthracenes

We report the synthesis and mesophase characterization of a series of novel hexaalkoxydibenzanthracenes to probe the effect of side-chain length variation and substituents on the mesophase temperature range. A series of hexaalkoxydibenz[a,c]anthracenes (2a–2i) with varying chain lengths were prepared by Suzuki coupling of the appropriate boronate ester with the corresponding dialkoxydibromonaphthalenes, followed by oxidative cyclization. Compounds 2a–2i were also brominated in the 10 and 13 positions to yield the corresponding dibromo series, 4a–4i. While none of the compounds, 2a–2i, exhibited columnar mesophases, all of the compounds in series 4a–4i did exhibit columnar phases over broad temperature ranges. To further investigate the effect of substituents on the mesomorphic properties of hexaalkoxydibenzanthracenes, we also prepared iodo-substituted 8, nitro-substituted 9, and amino-substituted 10. A comparison of the mesophase temperature range with previously reported compounds 3–7 shows that electron-withdrawing groups promote the formation of stable mesophases. However, our results also suggest that the substituents affect mesophase stability by participating in intermolecular contacts within the columnar stacks of the mesophase.

Synthesis and characterization of novel dibenz[a,c]anthracenedicarboxythioimides: the effect of thionation on self-assembly

The effect of thionation on the formation of columnar liquid crystalline phases of dibenzanthracenedicarboximides as well as their self-association in solution is described.