The first synthesis of the corrole ring by self-condensation of a monopyrrolic unit is reported. The reaction occurs only in the presence of cobalt ions; it leads to the formation of (triphenylphosphine)(5,10,15-triphenyl-2,3,7,8,12, 13,17,18-octamethylcorrolato)cobalt(III), [Co(OMTPC)PPh3] and represents the first example of interconversion between a porphyrinoid and a corrole structure. Crystals of [Co(OMTPC)PPh3].CH2Cl2 have been obtained by slow diffusion of methanol into a dichloromethane solution of the complex and have been characterized by single-crystal X-ray analysis. They crystallize in the triclinic system, space group P1BAR, with a = 10.628 (2) angstrom, b = 11.585(2) angstrom, c = 22.352(4) angstrom, alpha = 84.93(2)-degrees, beta = 78.56(2)-degrees, gamma = 72.93(2)-degrees, and Z = 2. The structure was solved by heavy-atom methods and refined by least-square techniques to R = 0.051 for 6377 unique data [F(o) > 4 sigma(F(o))]. The analysis reveals the substantial planarity of the macrocyclic ring. In the 23-atom core of the corrole moiety each atom shows an average displacement from the plane of best fit of 0.14 angstrom, with the largest deviations being +0.33 and -0.33 angstrom for C(2) and C(12), respectively. The synthesis of diphenyl derivatives of corrole : (triphenylphosphine) (5,10-diphenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III), [Co(5,10-OMDPC)PPh3], and (triphenylphosphine) (5,15-diphenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III), [Co(5,15-OMDPC)PPh3], is also reported. Plausible reaction pathways leading to the formation of the two isomers are discussed together with the spectral properties of the complexes.