The synthesis of 1,8-disubstituted biphenylenes by pyrolysis of azo compounds has been optimized. By means of a continuously working pyrolysis apparatus, the cis isomer 2 can be reliably produced on a gram scale. The chiral syn-[2.2]biphenylenophane 12 has been synthesized by an intermolecular cyclization reaction, subsequent oxidation of the sulfur atoms and pyrolytic extrusion of sulfur dioxide. In an analogous manner, the [2,2]biphenylophane 13 was obtained. The separation of the racemates of the hydrocarbons 12 and 13 could be achieved using a stationary chiral HPLC phase. Compound 12 preferentially adopts a syn conformation in the solid state. The CD spectra of 12 and 13 are compared.
The synthesis of the highly strained helical 4-tert-butyl-1,5,8-trimethylphenanthrene 6 was achieved by photochemically induced dehydrocyclization. The helical deformation of the aromatic carbon skeleton in the reported X-ray structure is found to be 36.6" which is the largest value found for a phenanthrene hydrocarbon. A systematic yuan tum chemical investigation of strained 4,S-substit u ted phenanthrene derivatives (R, R': F, Cl, methyl, tert-butyl) at ab initiu Hartree-Fock and semiempirical AM1 theoretical levels is presented. The geometrical parameters describing the strain in these helical molecules are compared with X-ray data from the literature and are found to be generally in good agreement. Substantial deviations between theory and experiment for the helical deformation angles are observed in the case of the chlorinesubstituted molecules (ca. 5") which indicates the importance of crystal packing effects. A prediction of the structure of the unknown 4,5-di-tert-butylphenanthrene 5, that could be detected by GC-MS, but has not been isolable so far is also given. The total strain energies of 5 and 6 are calculated to be 49.6 and 34.0 kcal mol-', respectively, and are distributed to non-bonded and aromatic ring deformation contributions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.