Synthetic aspects of 2,2 '-bisdipyrrins

The synthesis of open-chain, tetrapyrrolic 2,2'-bisdipyrrin ligands was inv estigated, starting from a variety of different pyrrolic and 2,2'-bipyrroli c precursors. Four important observations were made: (1) The solubility of 2,2'-bisdipyrrins can easily be tuned through the peripheral substituent pa ttern, allowing the aimed preparation of both well-soluble and hardly solub le tetrapyrroles. (2) meso-Arylsubstituted 2,2'-bisdipyrrins are easily ava ilable from respective p- and m-, but not o-functionalized dibenzoyl bipyrr oles due to sterical effects. (3) Unsymmetric derivatives can be obtained b y the stepwise acylation of 2,2'-bipyrroles and concomitant condensation re actions, using the new 5-benzoyl-3,3',4,4'-tetraethyl-2,2'-bipyrrole as the key intermediate. (4) meta-Nitrophenyl groups in the periphery of 2,2'-bis dipyrrins can be reduced to aminophenyl groups and further derivatized in a nalogy to a reaction cascade used in porphyrin chemistry, yielding superstr uctured 2,2'-bisdipyrrins. The synthetic schemes developed open the way for a large variety of tailor-made 2,2'-bisdipyrrin ligands. Copyright (C) 200 1 John Wiley & Sons, Ltd.