A Facile Preparation and Properties of (2E,4E,6E,8E)-1-(3-Guaiazulenyl)-3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexen-1yl)-2,4,6,8-nonatetraen-1-ylium Hexafluorophosphate

Reactions of guaiazulene (1) with all-trans- and 13-cis-retinals (2a and 2b) in methanol in the presence of hexafluorophosphoric acid at -10 °C for 1 h afforded the title monocarbocation compound 3 in 87-91% yield, respectively.