Reaction of guaiazulene with o-formylbenzoic acid in diethyl ether (or methanol) in the presence of hexafluorophosphoric acid: comparative studies on 1H and 13C NMR spectral properties of 3-guaiazulenylmethylium- and 3-guaiazulenium-ion structures

A facile preparation and the properties of 3-(3-guaiazulenyl)-2-benzofuran-1(3H)-one (5) are reported.