An efficient preparation, the structure and the properties of 1-isopropyl-4-(3-guaiazulenylmethylium)benzene hexafluorophosphate and tetrafluoroborate

Reactions of guaiazulene (1) with 4-isopropylbenzaldehyde in acetic acid in the presence of hexafluorophosphoric acid (and tetrafluoroboronic acid) at 25°C for 2 h under aerobic conditions quantitatively give the new title monocarbocation compounds, 1-isopropyl-4-(3-guaiazulenylmethylium)benzene hexafluorophosphate (4) and the tetrafluoroborate (5), which upon reaction with sodium methoxide dissolved in methanol in acetonitrile at 0°C for 20 min, respectively, afford as high as 92% isolated yield of 1-isopropyl-4-(3-guaiazulenylmethoxymethyl)benzene (8). The crystal structure of 5, as the first example of carbocations stabilized by azulenyl groups, and the characteristic and chemical properties of 4 and 5 are reported.