Regioselectivity in the Controversial Scholl Reaction of 1-Benzoylpyrene: Formation of a Five-Member Ring Is Not Unexpected

Intramolecular Scholl reaction of 1-benzoylpyrene (1) gave 8H-dibenzo[def,qr]chrysen-8-one (2) and 11H-indeno[2,1-a]pyren-11-one (3) in a 1:2 ratio. The structures of 2 and 3 were determined, using ¹H NMR, ¹³C NMR, and IR spectroscopies. A DFT B3LYP/6-311G(d,p) study of the reaction's arenium-cation mechanism of (E)-1 and (Z)-1 giving 2 and 3, respectively, indicated the reaction's regioselectivity and kinetic control. The analogous reaction of 1-(1′-naphthoyl)pyrene gave exclusively 13H-benz[4,5]indeno[2,1-a]pyren-13-one. Contrary to previous claims, the preferred formation of five-member rings in Scholl reactions is not unexpected.