Conjugated macrocycles related to the porphyrins. Part 2. Further synthetic and spectroscopic studies on difuryl analogs of the oxophlorins

The synthesis of three difuryl analogs of the oxophlorins is described. In common with the tetrapyrrolic oxophlorins, these compounds favor the keto tautomers and little, if any, of the enol tautomers are present in neutral solutions. Unlike the tetrapyrrolic systems, the difuryl oxophlorins give well resolved nmr spectra. Attempts to extend these studies to the synthesis of dithienyl oxophlorin analogs were unsuccessful.