Synthesis and characterization of the new 22‐π aromatic furan‐containing macrocycle, “ozaphyrin”

The new 22‐π, aromatic “pentaplanar” macrocycle, ozaphyrin (6), has been synthesized by a McMurry coupling of 5,5′‐diformyl‐4,4′‐dipropyl‐2,2′‐bipyrrole (1) with 2,5‐bis(5‐formyl‐4‐propyl‐2‐pyrrolyl)furan (5). This synthetic pathway to ozaphyrin and its characterization by ¹H nmr spectroscopy, uv‐visible spectroscopy, cyclic voltammetry, and X‐ray crystallography are described. The structure consists of layers of planar, staggered macrocycles stacked perpendicular to the α‐axis. Ozaphyrin crystallizes with four formula units in the monoclinic space group C⁵_2h‐P2₁/n in a cell of dimensions a = 10.481(7) Å, b = 17.353(17) Å, c = 18.726(12) Å, and β = 102.84(5)° (108 K). The structure has been refined on F² (5171 unique reflections, 411 variables) to R_w(F_o²) = 0.165. The conventional agreement index R(F) is 0.074 for the 3289 reflections have F_o²>2o(F_o²).