A Facile Preparation of (4-Aminophenyl)(3-guaiazulenyl)methylium Hexafluorophosphate: Comparative Studies on Spectroscopic, Chemical, and Electrochemical Properties of Monocarbenium Ion and p-Benzoquinodimethane Monoiminium Ion Compounds

Abstract Reaction of guaiazulene with 4-aminobenzaldehyde in CH3OH in the presence of hexafluorophosphoric acid at 25 °C for 2 h gives the title compound, with an equiv of HPF6, in 56% yield. Interestingly, a solution of the obtained new monocarbenium ion compound, forming a protonated amino group (4-H3N+PF6−), in CH3CN is allowed to stand at room temperature for 48 h, gradually converting to a new 4-(3-guaiazulenyl)methylene-2,5-cyclohexadiene-1-iminium hexafluorophosphate, completely. Furthermore, reductions of the above two products with NaBH4 in a mixed solvent of EtOH and CH3CN afford 4-amino-1-(3-guaiazulenylmethyl)benzene, selectively. Comparative studies on spectroscopic, chemical, and electrochemical properties of the monocarbenium ion compound with those of the 4-methylene-2,5-cyclohexadiene-1-iminium ion compound, are reported.