Polar effects in the decomposition of bis(3-alkoxyaroyl) peroxides. Synthesis of 8-alkoxy-6H-dibenzo[b,d]pyran-6-ones

The reaction of 4 substituted bis(3-alkoxybenzoyl) peroxides in neat phenols affords mainly 8-alkoxy-6H-dibenzo[b,d]pyran-6-ones and ortho-benzoyloxylation products of the phenol. E.g., 3,5-(MeO)2C6H3CO2O2CC6H3(OMe)2-3,5 and 4-MeC6H4OH give 41% dibenzopyranone I and 28% hydroxyphenyl benzoate II. Diaroyl peroxides without electron-releasing meta substituents afford only analogs of II. A mechanism involving monoelectronic oxidn. of the phenol by the peroxide and biaryl coupling by preferential addn. of the phenol radical cation to the ortho positions to the alkoxy group of the diaroyl peroxide is suggested