An efficient preparation, crystal structures, and properties of monocarbenium-ion compounds stabilized by 3-guaiazulenyl and anisyl groups

Reaction of guaiazulene (1) with 2-methoxybenzaldehyde (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h gives (3-guaiazulenyl)(2-methoxyphenyl)methylium hexafluorophosphate (5a) in 93% yield. Similarly, reaction of 1 with 3-methoxybenzaldehyde (3) or 4-methoxybenzaldehyde (4) under the same reaction conditions as for 2 affords (3-guaiazulenyl)(3-methoxyphenyl)methylium hexafluorophosphate (6) (91% yield) or (3-guaiazulenyl)(4-methoxyphenyl)methylium hexafluorophosphate (7) (97% yield). The crystal structures as well as the spectroscopic, electrochemical, and chemical properties of these monocarbenium-ion compounds, possessing interesting resonance forms, stabilized by the 3-guaiazulenyl and anisyl (i.e., 2-, 3-, or 4-methoxyphenyl) groups are reported.