Mechanistic insights into the malonoyl peroxide syn-dihydroxylation of alkenes

Rawling, Michael J. and Rowley, Julian H. and Campbell, Matthew and Kennedy, Alan R. and Parkinson, John A. and Tomkinson, Nicholas C. O. (2014) Mechanistic insights into the malonoyl peroxide syn-dihydroxylation of alkenes. Chemical Science, 5 (5). pp. 1777-1785. ISSN 2041-6520

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    A detailed mechanistic understanding of the malonoyl peroxide mediated dihydroxylation of alkenes is presented. The reaction is first order in both alkene and peroxide with stoichiometric water playing a dual role. An ionic mechanism is proposed and supported by the use of 18O isotopically labelled peroxide, a radical clock probe and DFT calculations. Hammett analysis suggests the reaction proceeds via a discrete carbocation intermediate which is consistent with the stereochemical outcome of the transformation. A subsequent Woodward-type 1,3-dioxolan-2-yl cation has been trapped in situ and the mechanism of hydrolysis defined by isotopic labelling studies. Stable reaction intermediates have been isolated and characterised by X-ray crystallographic analysis and minor competing reaction pathways identified.