Gold(III)-Mediated Contraction of Benzene to Cyclopentadiene: From p-Benziporphyrin to Gold(III) True Tetraarylcarbaporphyrin

The reaction of p‐benziporphyrin, sodium tetrachloroaurate(III) dihydrate, and potassium carbonate in dichloromethane yielded gold(III) 5,10,15,20‐tetraaryl‐21‐carbaporphyrin owing to the contraction of p‐phenylene to cyclopentadiene. This molecule is the very first representative of a true 5,10,15,20‐tetraaryl‐21‐carbaporphyrin complex where four trigonal donor atoms are involved in equatorial coordination. The contraction adds an unprecedented route to numerous organic transformations of aromatic compounds catalyzed by simple gold(III) compounds. p‐Benziporphyrin provided the unique environment to alter the fundamental reactivity of the benzene unit facilitating its contraction to cyclopentadiene. A pot of gold: An unprecedented contraction of a benzene to a cyclopentadiene unit, both set in a porphyrinoid environment, can be triggered by gold(III). The reaction affords the very first example of a meso‐tetraaryl 21‐carbaporphyrin complex that conserves perfectly the structural pattern of ubiquitous meso‐tetraarylporphyrins engaging coordination through trigonally hybridized carbon atoms (see scheme).