Azulene Functionalization by Iron-Mediated Addition to a Cyclohexadiene Scaffold

[Image: see text] The functionalization of azulenes via reaction with cationic η(5)-iron carbonyl diene complexes under mild reaction conditions is demonstrated. A range of azulenes, including derivatives of naturally occurring guaiazulene, were investigated in reactions with three electrophilic iron complexes of varying electronic properties, affording the desired coupling products in 43–98% yield. The products were examined with UV–vis/fluorescence spectroscopy and showed interesting halochromic properties. Decomplexation and further derivatization of the products provide access to several different classes of 1-substituted azulenes, including a conjugated ketone and a fused tetracycle.