Aryl pinacols and epoxides, respectively, are cleanly and in high yield converted via superacidic dehydrative cyclization to the corresponding condensed aromatics. Dehydrative cyclization of benzopinacol (1a), triphenylacetophenone (2), and tetraphenylethylene oxide (9) give 9,10-diphenylphenanthrene (3a) as the major product in acidic media stronger than H o = −11. Aryl pinacol 12a forms the condensed aromatic 13a as the major product in acidic media stronger than H o = −13.5. It is proposed that the dehydrative cyclizations to provide aromatics 3a and 13a occurs through dicationic intermediates. Substituted benzopinacols 1f, 1g, and 1j are prepared and give the corresponding phenanthrenes (3f, 3g, and 3j) in high yields. The regiochemistry of the cyclization of substituted benzopinacols is controlled by deactivating substituents on the aryl rings. Aryl pinacols (12a−d) derived from acenaphthenequinone and pinacol 15 also give condensed aromatics (13a−d and 16, repectively) with superacidic triflic acid.

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9,10‐diphenylphenanthrene product: 9,10‐diphenylphenanthrene