Straightforward route to trans-A2B-corroles bearing substituents with basic nitrogen atoms

We have developed a comprehensive methodology that affords regioisomerically pure trans-A(2)B-corroles bearing substituents with basic nitrogen atoms at meso positions. The corrole formation reaction involves the acid-catalyzed condensation of a dipyrromethane (DPM) and an aldehyde followed by oxidation with DDQ. The optimal conditions for this process were identified by extensive modifications of the previously developed conditions for the synthesis of trans-A(2)B-corroles with aromatic substituents. In particular three distinct sets of conditions were identified for various specific cases. Pyridine, quinoline and quinoxaline derived aldehydes as well as other aromatic aldehydes with tertiary amine groups in different positions were succesfully used in the condensation involving sterically hindered dipyrromethanes under the following conditions: (First step: CH2Cl2, [DPM] = 33 mM, [aldehyde] = 17 mM, [TFA] = 50 mM, 1h, room temperature, second step: neutralization with Et3N, CH2Cl2, dilution 26 times, 1.5 or 1.3 eqs. of DDQ versus DPM). A different set of conditions was developed for the condesation involving sterically unhindered dipyrromethanes: (first step: CH2Cl2, [DPM] = 33 mM, [aldehyde] = 17 mM, [TFA] = 17 mM, 5h, room temperature, second step: neutralization with Et3N, CH2Cl2, dilution 26 times, 1.5 or 1.3 eqs. of DDQ versus DPM). In this case only aldehydes with the formyl group directly adjacent to the heterocylic ring are efficient substrates; for the remaining aldehydes an extensive scrambling was observed. The condensation of pyridyldipyrromethanes with aldehydes bearing electron-withdrawing substituents (first step: CH2Cl2, [DPM] = 33 mM, [aldehyde] = 17 mM, [TFA] = 67 mM, 1h, room temperature, second step: neutralization with Et3N, CH2Cl2, dilution 26 times, 1.5 or 1.3 eqs. of DDQ versus DPM) leads to corroles in 2-11% yield depending on the position of the nitrogen atom. Finally, 10-(4-formylphenyl)-5,15-dimesitylcorrole was obtained and reacted with mesityldipyrromethane, giving the symmetrical corrole dyad in 14% yield. A total of 21 new corroles of type trans-A(2)B were prepared. Copyright (C) 2002 Society of Porphyrins & Phthalocyanines.