Acylation of Nickel <i>m</i><i>eso</i>-Tetraarylporphyrins: Porphyrin to Corrole Ring Contraction and Formation of <i>s</i><i>eco</i>-Porphyrins

Friedel−Crafts acylation of nickel meso-tetraarylporphyrins with aryl anhydrides, followed by air oxidation in the presence of pyridine, DMAP, and excess anhydride, produced corroles in 8−21% yields. Other products include a porphyrinic ketone, an additional corrole whose bridge has been retained as an acyl group attached to a pyrrole, and a lactone resulting from the insertion of an oxygen atom into an α,β-pyrrole bond. The ring contraction is best explained by a pinacolic rearrangement reminiscent of the one taking place in the formation of corrinoids, a benzoyloxy group replacing the acetic side chain found in the natural products.