Azulene

Derivatives

Vetivazulene or 4,8-dimethyl-2-isopropylazulene is obtained from vetiver oil. Guaiazulene or 1,4-dimethyl-7-isopropylazulene occurs naturally as a constituent of guaiac wood oil.

Structure

Azulene consists of a fused cyclopentadienyl anion which is aromatic and the likewise aromatic 6 pi electron tropylium cation. The observed dipole moment of 1.0 Debye is consistent with this picture.

Organic synthesis

For many years not many synthetic routes existed to azulene and the compound was therefore expensive. A recent contribution takes cycloheptatriene as starting material ^[1].

In naphth[a]azulenes, a tetrahelicene.

References

1. ^ Approach to the Blues: A Highly Flexible Route to the Azulenes Sébastien Carret, Aurélien Blanc, Yoann Coquerel, Mikaël Berthod, Andrew E. Greene, Jean-Pierre Deprés Angewandte Chemie International Edition Volume 44, Issue 32 , Pages 5130 - 5133 2005 Abstract
2. ^ Novel Synthesis of Benzalacetone Analogues of Naphth[a]azulenes by Intramolecular Tropylium Ion-Mediated Furan Ring-Opening Reaction and X-ray Investigation of a Naphth[1,2-a]azulene Derivative Kimiaki Yamamura, Shizuka Kawabata, Takatomo Kimura, Kazuo Eda, and Masao Hashimoto J. Org. Chem.; 2005; 70(22) pp 8902 - 8906; (Article) DOI: 10.1021/jo051409f Abstract