Macrocycle Contraction and Expansion of a Dihydrosapphyrin Isomer

Cyclization
of a pentapyrrane with two terminal β-linked
pyrroles afforded a dihydrosapphyrin isomer (1) with
the pyrroles linked in a unique β,α–α,β
mode, which was rather reactive, and thus it readily underwent a ring-contracted
rearrangement to a pyrrolyl norrole (2), and succeeding
ring expansion to a terpyrrole-containing isosmaragdyrin analogue
(4). 1, 2, and 4 contain the internal ring pathways with a minimum of 17, 15, and
16 atoms, respectively. 1, 2, and 4 are almost nonfluorescent, whereas the complex of 2 with Zn2+ shows a distinct NIR emission peak
at 741 nm. The unprecedented pyrrole transformation chemistry by confusion
approach is illustrated.