Combining Traceless Directing Groups with Hybridization Control of Radical Reactivity: From Skipped Enynes to Defect-Free Hexagonal Frameworks.

This work discloses the first general solution for converting oligoalkynes into polyaromatic polycyclic systems free of pentagonal defects. The efficiency and selectivity of this cascade originate from the combination of the Bu3 Sn-mediated TDG (traceless directing group) cascade transformations of skipped alkynes where the reactivity of the key radical precursor is tempered by hybridization effects. This approach ensures that the final structure consists of only six-membered rings. Practical implementation of this strategy is readily accomplished by incorporation of a suitably-substituted alkene as a final unit in the domino transformation. This strategy opens a new avenue for the controlled preparation of polyaromatic ribbons. The resulting ester functionality can be used for an additional Friedel-Crafts ring closure which effectively anneals two extra cycles with distinct electronic features to the extended aromatic system formed by the radical cascade.