Synthesis of Polyaromatic Hydrocarbons : Probing the Areneium Ion (Proton Transfer) Versus the Cation Radical (Electron Transfer) Mechanisms

DDQ/H+ oxidation system which is known to oxidize a variety of aromatic donors with oxidation potential as high as 1.8 V vs. SCE to the corresponding cation radicals can be effectively employed for the preparation of a variety of polyaromatic hydrocarbons. The development of DDQ/H+ oxidation system for oxidative C-C bond formation (or Scholl reaction) also allowed us to provide insight into the controversial arenium-ion (proton transfer) versus cation-radical (electron transfer) pathways for the Scholl reaction. A series of carefully-designed experiments provided evidences in support of cation radical pathway for the Scholl reaction. A detailed case study of oxidative cyclodehydrogenation of tetraveratrylethylene was also undertaken using a variety of traditional !-electron oxidants (such as FeCi}, NO+BF4-, and DDQ/H+), in order to further probe the arenium ion versus cation radical pathways for the Scholl reaction. This case study further asserted that oxidative C-C bond formations most likely occur via an electron transfer pathway rather than an arenium-ion mechanism. It was uncovered that reduction of electron-rich triarylmethanols usmg methanesulfonic acid (or trifluoroacetic acid) and borane-dimethyl sulfide complex (or triethylsilane) afforded a diarylmethane and an arene rather than expected triarylmethane. A careful investigation of the mechanism of this unexpected observation allowed us not only to demonstrate that triarylmethanes undergo acid-catalyzed Ar- CHAr2 bond cleavage but devise an alternative procedure using a non-protic Lewis acid (i.e. perfluorotriphenylboron) to access electron-rich triarylrnethanes from the corresponding triarylmethanols. Synthesis of a novel hexaarylbenzene-based receptor was also developed and was demonstrated that it binds six silver cations in its six circularly arrayed A-shaped cavities. The details of the four highly-related studies are described in chapters 1-4