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σ- versus π-Activation of Alkynyl Benzoates Using B(C6F5)3

School of Chemistry, Main Building, Cardiff University, Cardiff CF10 3AT, Cymru/Wales, UK
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Academic Editor: John Spencer
Molecules 2015, 20(3), 4530-4547; https://doi.org/10.3390/molecules20034530
Received: 8 February 2015 / Revised: 17 February 2015 / Accepted: 28 February 2015 / Published: 12 March 2015
(This article belongs to the Special Issue Recent Advances in Boron Chemistry)
We have prepared a range of alkynyl benzoates in high yields and have investigated their reactivities with the strong Lewis acid B(C6F5)3. In such molecules both σ-activation of the carbonyl and π-activation of the alkyne are possible. In contrast to the reactivity of propargyl esters with B(C6F5)3 which proceed via 1,2-addition of the ester and B(C6F5)3 across the alkyne, the inclusion of an additional CH2 spacer switches off the intramolecular cyclization and selective σ-activation of the carbonyl group is observed through adduct formation. This change in reactivity appears due to the instability of the species which would be formed through B(C6F5)3 activation of the alkyne. View Full-Text
Keywords: boron; trispentafluorophenyl borane; B(C6F5)3; Lewis acid; alkyne boron; trispentafluorophenyl borane; B(C6F5)3; Lewis acid; alkyne
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Bähr, A.; Wilkins, L.C.; Ollegott, K.; Kariuki, B.M.; Melen, R.L. σ- versus π-Activation of Alkynyl Benzoates Using B(C6F5)3. Molecules 2015, 20, 4530-4547.

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