A Simple Approach to Azoieues

Abstract

Recently, we demonstrated that the reaction of certain 2-phenylbicyclo-[1.1.0]butanes with rhoium dicrbonyl chloride dimer produced dihydroazulenes, which, on oxidation, were converted to azulenes.³. The utility of this process for the preparation of azulene derivatives was limited by the availability of the phenyl substituted bicyclo[1.1.0]butanes. Although the C-H insertion reaction, developed by Moore and coworkers⁴ for the preparation of 2-phenylbicyelo[1.1.0]butanes from dibromocyclopropanes, works very well, the required absence of cyclopropyl hydrogans, and the problems inherent in the preparation of the hexasubstituted dibromocyclopropane intermediates made the overall synthesis of azulenes by this route rather tedious. We now wish to report a simplified approach to the synthesis of azulenes whis has as one of the critical steps, the transition metal complex promoted rearrangement of a 2-phenylbicyclo[1.1.0]butane.