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Allylboration of carbonyl compounds is one of the most widely used methods in the stereoselective synthesis of natural products. However, these powerful transformations are so far limited to allyl- or crotylboron reagents; ring-strained substituents in the α-position have not been investigated. Such substrates would lead to an increase in strain energy upon allylboration and as such cause a significant increase in the activation barrier of the reaction. Indeed, no reaction was observed between an α-cyclopropyl allylboronic ester and an aldehyde. However, by converting the boronic ester into the much more reactive borinic ester, the allylboration proceeded well giving alkylidenecyclopropanes in high yield. This process was highly diastereoselective and gives rapid access to versatile alkylidenecyclopropanes and alkylidenecyclobutanes. The chemistry shows a broad substrate scope in terms of both the range of vinylcycloalkyl boronic esters and aldehydes that can be employed. The intermediate boronate complexes were also found to be potent nucleophiles, reacting with a range of non-carbonyl-based electrophiles and radicals, leading to an even broader range of alkylidenecyclopropanes and alkylidenecyclobutanes. Using 11B NMR experiments, we were able to track the intermediates involved, and DFT calculations supported the experimental findings.
|Number of pages||9|
|Journal||Journal of the American Chemical Society|
|Early online date||5 May 2021|
|Publication status||Published - 19 May 2021|
Bibliographical noteFunding Information:
D.P.H. thanks the EU for an H2020 Marie Sk?odowska-Curie Fellowship (840000). R.M. thanks the EU for an H2020 Marie Sk?odowska-Curie Fellowship (Grant 794053). V.F. thanks the University of Bristol for awarding the EPSRC Doctoral Prize Fellowship Grant ref EP/R513179/1.
D.P.H. thanks the EU for an H2020 Marie Skłodowska-Curie Fellowship (840000). R.M. thanks the EU for an H2020 Marie Skłodowska-Curie Fellowship (Grant 794053). V.F. thanks the University of Bristol for awarding the EPSRC Doctoral Prize Fellowship Grant ref EP/R513179/1.
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