Acid-catalyzed condensation of azulenes with 9-anthracenecarbaldehyde and the synthesis of (9-anthryl)di(1-azulenyl)methyl and (1-azulenyl)[10-(1-azulenyl)-9-anthryl]methyl hexafluorophosphates

Acid-catalyzed condensations of 1-methyl and 1,6-di-t-butylazulenes with 9-anthracenecarbaldehyde led us to unexpected 9-(1-azulenyl)-10-[(1-azulenyl)methylidene]-9,10-dihydroanthracenes 10a and 10b as major products, together with (9-anthryl)di(1-azulenyl)methanes 7a and 7b. Hydride abstraction from 7a, 7b, and 10b with DDQ afforded substituted (9-anthryl)di(1-azulenyl)methyl and(1-azulenyl)[10-(1-azulenyl)-9-anthryl]methyl hexafluorophosphates 6a, 6b . PF6- and 11b . PF6-, respectively. Their properties were fully characterized. The reaction of the 3-methyl derivatives 10a, however, did not afford the desired (3-methyl-1-azulenyl)[10-(3-methyl-1-azulenyl)-9-anthryl]methyl hexafluorophosphate (11a . PF6-), due to the low stabilities of 11a. While cations 6a and 6b prepared from 7a and 7b showed high stabilities with large pK(R+) values (10.7+/-0.1 and 12.4+/-0.1, respectively), cation 11b exhibited relatively low stabilities with the pK(R+) value of 5.0+/-0.1.