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

Treatment of methyl (Z)-2-alken-4-ynoates with the strong Lewis acid tris(pentafluorophenyl) borane, B(C6F5)3, yield substituted zwitterionic pyrylium borate species via an intramolecular 6-endo-dig 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.
Results based upon these data are published at http://doi.org/10.1039/c5dt03340c