3-Pyrrole-substituted 21,23-dithiaporphyrins

Ravikanth and coworkers have synthesized (S-pyrrole-substituted 21,23-dithiaporphyrins by refluxing 21,23-dithiaporphyrin with NBS in chloroform. (5-Aryl-substituted thiaporphyrin 238 (Scheme 94) has been obtained by condensing 3,4-disubstituted pyrroles 237 with thiophene diol 222 (X=S) under mild acid conditions (00CL480). 

Several porphyrin analogues with the pyrrolic nitrogens substituted by heteroatoms have been synthesized, but only the oxa analogues (23 X = O, Y = NH) are reported to form stable metal complexes (Figure 8). 60 Formation of a Zn complex of the thia analogue (23 X = S, Y = NH) requires the presence of a large excess of Zn" ion. An iron complex of dithiaporphyrin (23 X = Y = S) is also known. 

The incorporation of cyclic substituents, such as propane-1,3-diyldioxy, its ethyl and benzyl derivatives substituted at the (1-thiophene carbons of 21,23-dithiaporphyrins 240b and 21-monothiaporphyrins 241b (Scheme 95), has also been reported (04BCJ1173) by condensing the substituted thiophene diols 239b with benzaldehyde and pyrrole. The cyclic substituents at the (5-thiophene carbon atoms alter electronic properties of porphyrin. 

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