Restricted Rotation Involving the Tetrahedral Carbon. II. 2-Substituted 4,6,8-Trimethylazulenes

Abstract

Abstract 1-(1-Hydroxyethyl)-4,6,8-trimethylazulene (3) was prepared by the lithium aluminum hydride reduction of 1-acetyl-4,6,8-trimethylazulene, and by the reaction of methylmagnesium iodide with 1-formyl-4,6,8-trimethylazulene. 3 showed various melting points according to its crystallization conditions and the reaction solvent. Their IR spectra both in solid states and in solutions, the NMR spectra at various temperatures, and the results of X-ray diffraction studies led to a conclusion that this phenomenon is attributable to polymorphism. From the temperature dependence of the NMR spectra of the t-butyl protons of 1-t-butyl-4,6,8-trimethylazulene, the internal rotation around the CBu–Cazulene was concluded to be slow only at the lower temperature.