Lewis acid-base 1,2-addition reactions: synthesis of pyrylium borates from en-ynoate precursors

<p>Treatment of methyl (<em>Z</em>)-2-alken-4-ynoates with the strong Lewis acid tris(pentafluorophenyl) borane, B(C<small>₆</small>F<small>₅</small>)<small>₃</small>, yield substituted zwitterionic pyrylium borate species <em>via</em> an intramolecular 6-<em>endo-dig</em> cyclisation reaction. The supporting information, including figures of the NMR spectra for the compounds and reactions in the paper are included along with experimental procedures. X-ray data are included here which can be visualized using software for X-ray crystal structure determination/visualization which was used to characterise the compounds synthesised. Computation studies by DFT are included.</p><p>Results based upon these data are published at http://doi.org/10.1039/c5dt03340c <br></p><p><br></p>