Terpyrrole diformyl

The smallest pentapyrrolic is [20]pentaphyrin(1.0.1.0.0) (orangarin) 152. Acid-catalyzed condensation between hexamethyl terpyrrole 146 (Scheme 62) and diformyl bipyrrole 124 (1995CEJ56) furnishes 152. Compared to Huckel (18jt, 22it) aromatic species, 152 is 20jt antiaromatic as attested by its extremely broad absorption spectrum. While the pentapyrrolic aromatic species displays appreciable fluorescence, no appreciable fluorescence is seen for the antiaromatic species. 

The smallest pentapyrrolic expanded porphyrin to be reported to date is the so-called orangarin macrocycle (alternatively referred to as [20]pentaphyrin-(2.1.0.0.1) ). It was prepared in the form of the decaalkyl-substituted system 6.9 via an HCl-catalyzed condensation between the a-free terpyrrole 6.7 and the diformyl... 

An alternative synthesis of this type of molecule was also attempted. This approach, shown in Scheme 6.2.2, involved reversing the nucleophilic and electrophilic building blocks relative to those shown in Scheme 6.2.1. Thus, the diformyl terpyrrole 6.12 was condensed with the dicarboxyl-substituted dipyrrylmethane 6.13. 

---