Complex aromatic compounds with unusual shapes and structures

The syntheses and structural characterization of four large, chiral, rigid molecular bowls, a sterically congested in-methylcyclophane, and a giant polyphenylene macrocycle are described.; Four large, pentacyclic, steroidal ketones (C31H52O) were prepared from cholesterol in four-step syntheses via straightforward methods---Michael addition and Robinson annulation. From these four ketones, the corresponding four large, chiral, rigid, trimeric molecular bowls (C 93H150) were prepared by a triple aldol condensation promoted by TiCl4/ZnCl2. Large crystals of two of these molecules were obtained, but for some reason, those crystals did not yield X-ray structure solutions. Crystallographic work is still in progress.; A sterically congested in-methylcyclophane was prepared via the condensation of 1,8,13-tris(bromomethyl)-9-methyltriptycene and 1,3,5-tris(mercaptomethyl)benzene under basic conditions. The key intermediate in this synthesis was 1,8,9-trimethylanthracene, which was made by an efficient methylation of 1,8-dichloro-9-methylanthracene. The crystal structure of this in-methylcyclophane was determined, and it contains the sterically most crowded methyl group so far observed. Not only is the methyl group closer to a benzene ring than any other, but the C-CH3 bond distance is significantly shortened from standard values---a rare case of steric bond compression. Syntheses of a congested in-cyanocyclophane and an in-methoxycyclophane were also attempted, and, although unsuccessful, there is little doubt that 9-substituted triptycenes will be very useful building blocks for the preparation of a variety of cyclophanes with exceptionally close contacts between arenes and functional groups.; A tetrameric macrocyclic polyphenylene (C168H112), composed of four hexaphenylbenzene subunits (and previously prepared by X. Shen), was synthesized via three new synthetic pathways (olefin metathesis, McMurry coupling, and Wittig reaction). The products of these syntheses displayed clean 1H and 13C NMR spectra of the macrocycle for the first time. The synthesis of the corresponding hexameric macrocycle (C252H168) was also attempted.