Conformationally Locked Cyclo[2]Dipyrrins Linked with Anthracene Subunits: Synthesis and Chiroptical Properties

Abstract

Herein, we report the synthesis of anthracene‐containing twisted cyclo[2]dipyrrin 1 by utilizing a non‐planar building block, 1,5‐dipyrrylanthracene (1,5‐DPA). The non‐planar nature of the macrocycle enhanced the solubility and helped in structural characterization. Macrocycle 1 adopts a twisted ‘figure of eight’ conformation stabilized by strong intramolecular H‐bonding interactions and exists as a pair of helical enantiomers, as revealed by X‐ray crystallographic analysis. More importantly, the sterically locked structure enabled facile optical resolution using chiral HPLC. The (P,P) and (M,M) enantiomers show moderate chiroptical properties, such as absorption dissymmetry factors |gabs| in the order of 10−3, and luminescence dissymmetry factors |glum| of 3.8×10−3 and 2.9×10−3 at 702 nm, respectively.

Porphyrinoid framework embedded with polycyclic aromatic hydrocarbons: new synthetic marvels

“…Very recently, a few reports on the anthracene unit as a part of porphyrinoid frameworks have been published. 37–39 Cho and co-workers reported the synthesis of the first example of meso -fused anthriporphyrin 71 , as shown in Scheme 13. 37 9-Bromo-2-methyl anthracene 73 was subjected to bromination with NBS in CCl 4 to afford dibromide 74 , which was further oxidized with N -methylmorpholine N -oxide in THF at 50 °C to produce aldehyde 75 .…”

“…Gokulnath and co-workers 39 reported the synthesis of anthracene-based twisted cyclo[2]dipyrrin 83 as presented in Scheme 15. 1,5-Dibromo anthracene 84 was coupled with N -Boc pyrrole 2-boronic acid under Suzuki coupling conditions to afford compound 85 , which was then subjected to deprotection with ethylene glycol to yield 1,5-dipyrrylanthracene 86 in 73% yield.…”

Resolution of Expanded Porphyrinoids: A Path to Persistent Chirality and Appealing Chiroptical Properties

“…Very recently (2023), Gokulnath and co-workers reported the synthesis of an anthracene-embedded cyclo[2]dipyrrin, 6, built up from a 1,5-dipyrrylanthracene synthon. [23] The specific substitution mode of the anthracene building block in 6 is thought to lead to unfavorable steric constraints, resulting in a twisted figure-of-eight architecture (Figure 5). This structure bears resemblance to what had been described previously for certain helical hetero-1,5-naphthiporphyrins.…”