Oxygenation of 2,6-Di-tert-butylphenols Bearing an Electron-Withdrawing Group in the 4-Position

Article abstract of DOI:10.1021/jo00133a009

Co(Salpr), a five-coordinate cobalt (II) Schiff base complex, has been found to promote oxygenation of 2,6-di-tert-butylphenols bearing an electron-withdrawing group in the 4-position, leading to dioxygen incorporation exclusively into the ortho position of the phenols. 4-Acyl-2,6-di-tert-butylphenols (1) and their oxime O-methyl ethers (2) gave the corresponding 6-hydroperoxy-2,4-cyclohexadienone derivatives 3 and 4 quantitatively.Schiff bases 10 derived from 3,5-di-tert-butyl-4-hydroxybenzaldehyde, on the other hand, gave unexpected products, 1,2-dihydropyridine derivatives 11, cyclopentadienone 12, and epoxy-o-quinol 13.The structure of dihydropyridine 11a was determined by X-ray analysis. 2,6-Di-tert-butyl-4-cyanophenol gave 2,5-di-tert-butyl-3-cyano-2,4-cyclopentadienone in good yield.The formation of these products can be understood to result from intramolecular decomposition of the corresponding o-peroxidic intermediate.Phenols 2 were readily oxygenated in t-BuOH containing t-BuOK to give epoxy-o-quinols 7 in excellent yield, although the other phenols examined were unsusceptible to oxygenation under various basic conditions.