Dienone Tautomers of 4-Alkoxy-2,6-di-tert-butylphenols.
Generation and isolation of 4-alkoxycyclohexa-2,5-dienones 9, the tautomeric forms of the title phenols (10), is described. They are generated efficiently by the Ag ion mediated reaction of 4-bromocyclohexa-2,5-dienone 3b with simple alcohols, although they can be irreversibly isomerized into 10 under the reaction conditions. Crude materials with high amounts of 9 can be obtained by conducting the reaction with AgClO(4) in the presence of Na(2)CO(3) or with AgOCOCF(3) and by interrupting the reaction shortly after the formation of 9 is complete. The AgOCOCF(3) reaction produces labile 4-(trifluoroacetoxy)cyclohexa-2,5-dienone 11 also, the formation of which becomes significant as the alcohol becomes bulky. All of 9 prove to be very much susceptible to the prototropic rearrangement into 10 by catalysis with base, acid, or SiO(2). Crude dienones 9 can be conveniently prepared directly from phenol 6 by treatment for a short time with Br(2) in alcohols containing AgClO(4) and Na(2)CO(3). A one-pot synthesis from 6 of 4-oxyfunctionalized 2,6-di-tert-butylphenols, including 10, is also described.
Omura
Kanji
K
College of Nutrition, Koshien University, Momijigaoka, Takarazuka, Hyogo 665, Japan.