Bipyrrole pyrrolyl

Bis(2-pyrrolyl) sulfides, prepared from the reaction of the pyrrole with sulfur dichloride, are useful precursors in the synthesis of corroles and related compounds, as it is possible to cause the extrusion of the sulfur atom with the consequent formation of a bipyrrolic unit within the macrocycle <72JCS(P1)1124). 

It is worth mentioning that an alternative 3 + 2 synthetic approach to sapphyrin has been reported. Specifically, it was found that the alkyl-substituted sapphyrin 5.19 could be prepared via the acid-catalyzed condensation of pyrrolyl-bipyrrole 5.27 with diformyl dipyrrylmethane 5.28 (Scheme 5.1.5). Following oxidation with air and chromatographic purification, this method affords a 35% yield of the desired sapphyrin. Unfortunately, this method has yet to find any kind of general applicability. This is most likely a reflection of the fact that the needed pyrrolyl-bipyrrolic precursors are hard to make. 

Prior to developing the above synthesis, Sessler and coworkers discovered a different route to meso-axy sapphyrins. This synthetic strategy, like so many in the area of sapphyrin-related research, is based upon a reaction that was not initially intended to produce sapphyrins. Specifically, it involves the reaction between bis(pyrrolyl)bipyrrole 5,38 and diformyl dipyrrylmethane 5.39, and was found to produce, quite unexpectedly, sapphyrin 5,41 in ca. 5% yield, with none of the intended hexapyrrolic macrocycle 5,40 being detected (Scheme 5.2.3). It was thus considered that such a 4 + 2 = 5 approach might prove useful for the synthesis of we o-phenyl sapphyrins. This indeed proved to be the case. In fact, this strategy has... 

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