PREPARATION OF CONDENSED AROMATICS BY SUPERACIDIC DEHYDRATIVE CYCLIZATION OF ARYL PINACOLS AND EPOXIDES

Aryl pinacols and epoxides, respectively, are cleanly and in high yiel d converted via superacidic dehydrative cyclization to the correspondi ng 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 strong er than H-o = -11. Aryl pinacol 12a forms the condensed aromatic 13a a s the major product in acidic media stronger than H-o = -13.5. It is p roposed 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 substituen ts on the aryl rings. Aryl pinacols (12a-d) derived from acenaphtheneq uinone and pinacol 15 also give condensed aromatics (13a-d and 16, rep ectively) with superacidic triflic acid.