Iodine-Mediated Aromatization of Himachalenes: Synthesis of Dehydro-7,8-arylhimachalene

Abstract: Dehydro-7,8-aryl-himachalene is a desired natural benzocycloheptene sesquiterpene found in the essential oil of Atlas cedar (Cedrus atlantica) in minor quantities. Herein, we report a simple and environmentally benign synthesis of this molecule via the aromatization of himachalene mixture (the major constituent of the same oil). The synthesis of the desired compound has been achieved by iodine/DMSO-mediated aromatization. The synthesized product has been characterized using MS spectrometry and NMR spectroscopy data. The treatment of the himachalene mixture with iodine led to the formation of dehydro-7,8-arylhimachalene, along with other rearrangement products catalyzed by the hydroiodic acid formed in situ. The use of DMSO as a co-solvent enabled the elimination of the acid formed and the regeneration of iodine. The optimization of the reaction conditions led to the formation of the desired product with a good yield. The present study highlights the development of a simple and environmentally benign method for the synthesis of a natural benzocycloheptene-based sesquiterpenoid in large quantities in order to explore its biological and chemical properties.