Reactions of 4-hydroxycyclohexa-2,5-dienones under acidic conditions

Abstract

The 4-hydroxy-4-phenyl-2,6-di-t-butylcyclohexa-2,5-dienone (2) undergoes reaction in acidic conditions to give, inter alia, derivatives of an arene-1,2-diol. In poorly nucleophilic media, the 1,1′-biphenyl-4-ol (16) and the 5-phenyl-o-benzoquinone (37) are the main products. Isolation of the 4-(2-methylpropyl)cyclohexadienone derivatives (41) and (42) provides the first examples of intermolecular trapping of a four-carbon unit. The products are consistent with the intervention of the phenoxenium ion (44); the formation of the 2-methyl-1,3-benzodioxole (43) testifies to the intermediary of such a powerful oxidant. Whereas the 4-phenyl-2-t-butyl-p-quinol (5) gave a complex mixture from which only the 1,1′-biphenyl-4-ol derivative (24) was isolated, the 2,6-di-isopropyl- and 2,6-dimethyl-analogues (4) and (6) afforded mainly the arene-1,3-diol derivatives (48) and (47), respectively. The 4-methyl-2,6-di-t-butyl-p-quinol (7) gave products [e.g.(28) and (29)] arising from nucleophilic attack on an intermediate p-quinone methide; dimers were the major products in the absence of a good nucleophile.