The Reaction of the 2,6-Di-tert-butyl-4-methylphenoxy Radical with Phenols

Article abstract of DOI:10.1021/jo00003a006

Dimer 3 dissociates in solution to give the phenoxy radical 4.When solid 3 is dissolved in a solution of phenol 11a, radical 4 dehydrogenates the phenol to afford phenol 5 and phenoxy radical 12.Radical 12 couples with more 4 to afford principally bis(cyclohexadienone) 16a and a minor amount of the dimeric bis(cyclohexadienone) 13.The preferential formation of 16a over 13 is explained as the result of a solvent-cage reaction.Compounds 13 and 16a are isomerized in the presence of silica gel or triethylamine to 4,4'-dihydroxybiphenyl 14 and phenolic dienone 17a, respectively.Compound 13 is relatively stable in hexane at 30 deg C, while 16a slowly dissociates under these conditions to afford parent radicals 4 and 12.If 11a is present, radical 4 either recombines with 12 or dehydrogenates the phenol.Two radicals of 12 generated by the dissociation of 16a and the subsequent dehydrogenation of 11a couple to give 13.Therefore, dissolving 3 in hexane containing excess 11a and keeping the resulting solution at 30 deg C results in the preferential formation of 13.Dissolving 3 in triethylamine containing phenols 11 or 21 similarly affords dienones 17 or 23.The yields of these dienones increase with increasing electron-donating capability of the substituent of the phenol ring.