The Double-Protonation of Dihapto-Coordinated Benzene Complexes: An Enabling Strategy for Dearomatization Using Aromatic Nucleophiles

Friedel Crafts Arylation (the Scholl reaction) is the coupling of two aromatic rings with the aid of a strong Lewis or Bronsted acid. This historically significant C-C bond forming reaction normally leads to aromatic products, often as oligomeric mixtures, dictated by the large stabilization gained upon their rearomatization. In this preliminary communication, we demonstrate how the pre-coordination of benzene by tungsten disrupts the natural course of this reaction sequence, allowing for Friedel-Crafts Arylation without rearomatization or oligomerization. Subsequent addition of a nucleophile to the coupled intermediate leads to functionalized cyclohexenes. The key feature of this reaction is a tungsten complex bound through two carbons, which enables a rarely observed double protonation of the bound benzene, and subsequent coupling to the second arene without the need of precious metal or Lewis acid catalysts.