Iron(III)-Mediated Bicyclization of 1,2-Allenyl Aryl Ketones: Assembly of Indanone-Fused Polycyclic Scaffolds and Dibenzo[a,e]pentalene Derivatives.

The rapid construction of three-dimensional fused carbocycles is a key challenge in synthetic chemistry. Herein, an unprecedented and practical tandem Nazarov/oxidative umpolung 4π-ring closure of readily available 1,2-allenyl aryl ketones mediated by iron(III) chloride has been developed, furnishing a new family of indanone-fused molecular architectures in moderate to excellent yields. The indanone-containing blocks can be efficiently converted to unsymmetrical dibenzo[a,e]pentalenes. Significantly, divergent synthetic applications have been achieved to provide densely functionalized polycyclic arrays.