Aryl nitroporphycenes and derivatives: First regioselective synthesis of dinitroporphycenes

The nitration reaction of 2,7,12,17-tetraphenylporphycene has been studied. The use of AgNO₃ and a mixture of acetic acid and 1,2-dichloroethane as a mild nitrating system provides an optimized preparation of 9-nitro-2,7,12,17-tetraphenylporphycene and a regioselective synthesis of 9,20-dinitro-2,7,12,17-tetraphenylporphycene. While 25 min of reaction are needed to obtain the mononitrated compound, 4 h are necessary to yield a mixture of 9,20-dinitro and 9,19-dinitro 2,7,12,17- tetraphenylporphycene in a proportion of 3 to 1. From this mixture, the geometric isomers can be isolated by fractional crystallization. 9-Nitro-2,7,12,17-tetraphenylporphycene can be reduced to the corresponding amino derivative, which is the starting material to obtain 9-(glutaric methylesteramide)- 2,7,12,17-tetraphenylporphycene, a versatile derivative useful for conjugation.