Insights into Pinacol Rearrangement: Oxidative versus Acid‐Catalyzed Mechanism. Issue 38 (8th October 2021)

• Record Type: Journal Article
• Authors: Monopoli, Antonio; Casiello, Michele; Fusco, Caterina; D'Accolti, Lucia; Ciminale, Francesco; Nacci, Angelo
• Is Part Of: ChemistrySelect. Volume 6:Issue 38(2021)
• Page Start: 10238
• Page End: 10242
• Publication Date: 2021-10-08
• Subjects: aminium salt -- intramolecular proton transfer -- oxidative cleavage -- pinacol rearrangement; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.202102552
• Languages: English
• ISSNs: 2365-6549

Abstract

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. Abstract : The reaction of trans ‐1, 2‐bis(4‐methoxyphenyl)cyclohexane‐1, 2‐diol with excess amounts (4 eq.) of tris(2, 4‐dibromophenyl)aminium hexachloro‐antimonate affords only 1, 6‐bis(4‐methoxyphenyl) hexane‐1, 6‐dione through an oxidative cleavage . An analogous reaction of the corresponding cis‐ diol, gives mainly 2, 2‐bis(4‐methoxyphenyl)cyclohexanone, whose formation might proceed through an oxidative rearrangement alternative, at least in part, to the classic acid catalysed pinacol rearrangement.