Bromination of Azulene Derivatives with Sodium Monobromoisocyanurate

Abstract

Methyl azulene‐1‐carboxylate (2) and 1‐acetylazulene (3) were treated with sodium monobromoisocyanurate (SMBI) (1) to give 3‐bromo‐substituted azulenes 5 and 6, respectively. The brominations in dichloromethane gave the brominated products in low yields, while the reactions in dichloromethane–water gave the products in high yields. This indicates that SMBI (1) was hydrolyzed in the presence of water to generate hypobromic acid, which accelerated the bromination as a source of bromonium cation. The protic ethanol also promoted the reactions. The brominations of 1‐methyl‐, 1‐ethyl‐, and 1‐propylazulenes 10a–c were carried out to afford compounds 11a–c in low to moderate yields.

Keywords:

• Azulene
• SMBI
• Brominating agent
• Bromination
• Protic solvent

Acknowledgment

We are grateful to Dr. Hideo Suzuki, Nissan Chemical Industries, Ltd., for the donation of the reagent SMBI and his discussion.