acase@tulane.edu / The syntheses and structural characterization of 3-arylimino steroids, tribenzodecacyclene, hexabenzodecacyclene, and a new class of twisted chiral polycyclic aromatic compounds, the “hairpin furans” are described. In the hope of generating a new class of materials with large optical rotations, various arylamines were condensed with cholest-4-ene-3,6-dione (14) to give 3-arylimino steroids. These compounds possess moderately high specific rotations ([α]D ~ 300-800) and strong circular dichroism. One such derivative, 3-(4-methoxyphenylimino)cholest-4- en-6-one (15), crystallizes as the (E)-imine and upon dissolution undergoes mutarotation to an equilibrium mixture of (E)- and (Z)-isomers with a half-life of approximately 1 h at room temperature, as judged by both NMR spectroscopy and polarimetry. High-temperature, TiCl4-catalyzed, triple aldol condensations of aceanthrenone 26 and acenaphthacenone 27 gave tribenzodecacyclene 18 and hexabenzodecacyclene 19, respectively, in yields of 16% and 0.8%, respectively. Compound 18 is a red, crystalline solid that is stable under ordinary conditions; its X-ray structure reveals it to be a strongly pitched, C3-symmetric, molecular propeller. In contrast, the more highly strained compound 19 is a blue-black solid whose solutions are unstable to air and light. Its simple NMR spectra, as well as HDFT calculations, indicated that it is a D3-symmetric molecular propeller. The thermal reaction of two cyclopentadienones with 5,5’-binaphthoquinone or 6,6’-dimethoxy-5,5’-binaphthoquinone in refluxing nitrobenzene (210 °C) gives, in a single synthetic step that includes two Diels-Alder additions, two decarbonylations, and two dehydrogenations, giant biaryl bisquinones (compounds 42, 50, 52, 53 and 62). However, when two cyclopentadienones react with 6,6’-dimethoxy-5,5’- binaphthoquinone in nitrobenzene at higher temperatures (250-260 °C), the resulting products are molecular ribbons composed of two twisted aromatic systems fused to a heteropentahelicene (49, 51, and 54). These molecules are representatives of a new class of chiral polycyclic aromatic compounds, the “hairpin furans”. Interestingly, reheating a dimethoxy-substituted giant biaryl (e.g., 52) in nitrobenzene at 260 °C does not yield the corresponding hairpin furan, and the mechanistic studies indicate that some intermediate or byproduct of the synthesis of the giant biaryls is a reagent or catalyst necessary for the conversion of the dimethoxybiaryl to the furan. / 1 / Xin Geng
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_59122 |
| Date | January 2016 |
| Contributors | Geng, Xin (author), Pascal, Robert (Thesis advisor), School of Science & Engineering Chemistry (Degree granting institution) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | electronic, 183 |
| Rights | No embargo, Copyright is in accordance with U.S. Copyright law. |
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