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Oxidative Rearrangement of Cyclic Tertiary Allylic Alcohols with IBX in DMSO

Masatoshi Shibuya, Shinichiro Ito, Michiyasu Takahashi and Yoshiharu Iwabuchi*

*Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan, Email: iwabuchimail.pharm.tohoku.ac.jp

M. Shibuya, S. Ito, M. Takahashi, Y. Iwabuchi, Org. Lett., 2004, 6, 4303-4306.

DOI: 10.1021/ol048210u


Abstract

A practical and environmentally friendly method for the oxidative rearrangement of five- and six-membered cyclic tertiary allylic alcohols to α,β-unsaturated β-disubstituted ketones by IBX in DMSO is described. Several conventional protecting groups (e.g., Ac, MOM, and TBDPS) are tolerated.

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Details

The document describes a practical and environmentally friendly method for the oxidative rearrangement of five- and six-membered cyclic tertiary allylic alcohols to β-disubstituted α,β-unsaturated ketones using the IBX/DMSO reagent system. This method is an alternative to the traditional use of hazardous oxochromium(VI)-based oxidants like PCC and PDC. The study found that 1.5 equivalents of IBX in DMSO at room temperature gradually promoted the oxidative rearrangement, with increased efficiency at 55°C. The method was tested on various substrates, showing good yields and compatibility with several protecting groups. The study also explored the reaction mechanism, suggesting two possible pathways involving either solvolysis to an allylic cation or formation of a tertiary iodic ester. The IBX-mediated oxidative rearrangement was found to be effective for five- and six-membered cyclic tertiary allylic alcohols but less so for acyclic substrates. The method offers an eco-friendly and user-friendly alternative for synthesizing complex molecules. Supporting information, including experimental details and NMR spectra, is available online.


Key Words

IBX, Oxidation (Alkenes, Alcohols), Enones, Oxidative Rearrangement


ID: J54-Y2004-980