Macrocycles encompassing four pyrrole rings are traditional motifs in biochemical and synthetic light harvesting and catalysis. Inaba et al. document a strained, smaller analog with three pyrroles. Their route cyclized a linear hexaketone precursor through condensation, restored the six carbonyls through an oxidation–discount sequence, and then aminated it to carry out the pyrroles. Crystallography highlighted the high stress inherent in the structure, which rapid underwent a hoop-opening dimerization in acidic resolution to carry out a calix pyrrole. The implications support to indicate why the tetrapyrrole structure is the smallest of those macrocycles that’s readily noticed.
J. Am. Chem. Soc. 10.1021/jacs.1c06331 (2021).