Preparation of Condensed Aromatics by Superacidic Dehydrative Cyclization of Aryl Pinacols and Epoxides^1a

Abstract

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.

Palladium‐Catalyzed Annulation of vic‐Bis(pinacolatoboryl)alkenes and ‐phenanthrenes with 2,2′‐Dibromobiaryls: Facile Synthesis of Functionalized Phenanthrenes and Dibenzo[g,p]chrysenes

“…The scope of the annulation reaction leading to functionalized dibenzo-[g,p]chrysenes (5) is summarized in Table 2. Various dibenzo-[g,p]chrysenes (5) substituted with electron-donating and electron-withdrawing groups are not easily accessible by previous methods, [19] but they were isolated in moderate to good yields by using our annulation chemistry. Notably, fluorinated dibenzo[g,p]chrysenes 5 ad, 5 bd, 5 cd, 5 dd, and 5 fd were generally produced in high to excellent yields ( Table 2, entries 3, 6, 8, 9, and 11).…”

Reactions of acenaphthenequinone and aceanthrenequinone with arenes in superacid

“…Similar conversions were described involving dehydrative cyclizations of aryl-pinacols and 2,2,2-triphenylacetophenone (20). 10 In the superacid promoted dehydrative cyclization of 20, experimental evidence suggested the involvement of an O,O-diprotonated superelectrophile. An analogous diprotonated species (21) is proposed in the dehydrative cyclization (eq 5), with an initial step involving a phenyl migration to the carboxonium position.…”

Superelectrophiles: Recent Advances

“…A mechanism was proposed involving superelectrophile 91 . It has also been demonstrated that tetraaryl-1,2-ethane dications give phenanthrene products in high yields [ 69 , 70 ]. Precursors 93-96 may all be ionized to the dication 97 by the action of acids or oxidants.…”