Synthesis of naphthalenes using acid-catalyzed ring-opening and recyclization of 3-acetyl-5,5-diaryl-2-methyl-4,5-dihydrofurans. Isolation of intermediates

3-Acetyl-5,5-diaryl-2-methyl-4,5-dihydrofurans were heated in concentrated hydrochloric acid to give the 4-aryl-1-methylnaphthalenes in high yields. T he same reaction was carried out in hydrochloric acid diluted with acetonit rile to give the 5,5-diaryl-4-penten-2-ones (87-96%), while treatment of th e dihydrofurans with p-toluenesulfonic acid in acetonitrile afforded the 3- (2,2-diarylethenyl)-4-hydroxy-3-penten-2-ones (73-91%) which were transform ed in diluted hydrochloric acid into the 5,5-diaryl-4-penten-2-ones. It was demonstrated that the 3- and 4-penten-2-ones were intermediates of the 3-a ryl-1-methylnaphthalenes since the 3- and 4-penten-2-ones were easily conve rted into the corresponding naphthalenes in concentrated hydrochloric acid. The UV irradiation of the dihydrofurans in the presence of hydrochloric ac id quantitatively gave the 2-acetyl-4-aryl-1methylnaphthalenes (94-97%) via the same 3-penten-2-one intermediates. (C) 2001 Elsevier Science Ltd. Al] rights reserved.