A Convenient Synthetic Route to Benz[cd]azulenes: Versatile Ligands with the Potential To Bind Metals in an η5, η6, or η7 Fashion

A facile method for preparing the 2H-benz[cd]azulene system, based upon an elaboration of the guaiazulene framework, is presented. Aerial oxidation to the corresponding 8-(2-propylidene)-benz[cd]azulene, and also cycloaddition reactions with tetracyanoethylene (TCNE), are described. The first X-ray crystal structure of a 2H-benz[cd]azulene, as an eta6-coordinated Cr(CO)3 complex, is reported.