Insights into Pinacol Rearrangement: Oxidative versus Acid‐Catalyzed Mechanism

Abstract Reactions of both diastereomers of 1,2‐bis(4‐methoxyphenyl)cyclohexane‐1,2‐diol ( 1 d ) with tris(2,4‐dibromo‐phenyl)aminium hexachloroantimonate as the oxidant in dichloromethane have been investigated to get evidence on the possibility that a pinacol rearrangement may be oxidatively activated rather than acid‐catalyzed . Relevant to this, we found that in the presence of an excess (4 eq) of oxidant, cis‐ 1 d afforded the rearrangement product 2,2‐bis(4‐methoxyphenyl)cyclohexanone in large amounts, while trans‐ 1 d gave exclusively the oxidative cleavage product 1,6‐bis(4‐methoxyphenyl)hexane‐1,6‐dione. Stereospecific implications explaining the reactivity difference between the two diastereomeric radical cation intermediates, cis‐ and trans‐ 1 d ⋅+ , are discussed.