Scholl reaction, aluminum chloride

Since the polycyclic ketones required for the Scholl reaction are generally prepared by the Friedel-Crafts synthesis, the two reactions can be combined thus, passing a stream of oxygen into an aluminum chloride-sodium chloride melt containing 1-benzoylpyrene and /7-toluoyl chloride yields 3-methyl-8,16-... 

When aromatic hydrocarbons are treated with aluminum chloride the autocondensation is accompanied by side reactions (ring contraction, partial hydrogenation, etc.) reactions of phenyl and naphthyl ethers are, however, smoother, and Scholl and Seer278 obtained good yields of 4,4 -diethoxy-l,l -binaphthalene from 1-ethoxynaphthalene and aluminum chloride in nitrobenzene. 

Cyclodehydrogenation of heterohelicenes. Several syntheses of coronene and related polynuclear hydrocarbons involve cyclodehydrogenation with aluminum chloride or sodium aluminum chloride to form aryl—aryl bonds (Scholl reaction). In their studies on the synthesis of heterohelicenes, Wynberg and... 

Nitronium salts are capable to induce the OCA reaction via generation of aryl radical-cations, even with relatively electron-poor arenes, such as benzene [105]. Namely, NOBF4 in catalytic amount (1-5 mol%) efficiently catalysed the oxidative coupling reactions of polyalkoxybenzenes in dichloromethane (containing 20% trifluoroacetic acid) under exposure to air affording the corresponding biaryls in almost quantitative yields [105]. Finally, oxidative couplings of arenes can be accomplished under the classical Scholl reaction conditions [106]. For example, 1-ethoxynaphthalene (419) was coupled to binaphthyl 420 by reaction with anhydrous aluminum chloride and nitrobenzene (as oxidant) in 65% yield, Scheme 28. 

While the original Scholl conditions called for both a Lewis and protic acid, research by Kovacic and Kyriakis into the role of oxidizing agents (that facilitate the formation of radical cations) in the Scholl reaction led to the observation that benzene (12) when reacted in the presence of a heterogeneous mixture of anhydrous aluminum chloride and copper chloride afforded poly(para-phenylene) (13). It is important that Ihis reaction was conducted under mild conditions (25-35 °C) and was complete in only 2 h. As discoverers of one of the first Scholl reactions conducted under mild conditions, Kovacic and Kyriakis have greatly increased the synthetic utility of this reaction. 

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