Improved Synthesis of ortho‐Phenylene‐bridged Cyclic Tetrapyrroles and Oxidative Fusion Reactions Toward Substituted Tetraaza[8]circulenes

Abstract

Hetero[8]circulenes have emerged as novel functionalized heteronanographenes that show various promising functions such as bright fluorescence, charge transporting, and redox reactivities. One of the effective synthetic strategy is the fold‐in type oxidative fusion reaction of ortho‐phenylene‐bridged cyclic tetrapyrroles, whose construction, however, is not well‐sophisticated in terms of reproducibility and possibility for versatile derivatization. In this paper, a “reverse” coupling strategy has been developed, which enabled synthesis of opp‐type low symmetric analogues of cyclic tetrapyrroles. Oxidative fusion reaction conditions to afford tetraaza[8]circulenes have also been reinvestigated and improved. Substituent effects of cyclic tetrapyrroles and tetrabenzotetraaza[8]circulenes are studied for solid‐state structures and packing structures, redox potentials, and optical properties.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“… Reagents and conditions: (a) 462 DDQ, TfOH, DCM, rt, 10 min–6 h; (b) 1-iodooctane, NaH, DMSO, 50 °C, 38 h; (c) m -CPBA, CHCl 3 , reflux, 3 h; (d) aniline or 4- tert -butylaniline, KHMDS, dioxane, 90 °C, 24 h; (e) 463 diphenylmethane, KHMDS, dioxane, 90 °C, 24 h; (f) BAHA, DCM, rt, 30 min; (g) 464 SPhos Pd G2, K 3 PO 4 , THF/H 2 O, 60 °C, 12 h; (h) DDQ, Sc(OTf) 3 , toluene, darkness, reflux, 2–5 h. …”

“…In 2021, the same group presented an improved synthesis of the o -phenylene-spaced cyclic tetrapyrroles 248.7a – d . 464 Hence, the boronate-containing dipyrrolylbenzene 248.6 underwent Suzuki–Miyaura cross-coupling with the appropriate ortho -dibromobenzenes to give the desired macrocycles 248.7a – d in 7–11% yield. In comparison, the previous “reverse” coupling strategy suffered from lower yields attributed to the low stability of the corresponding dibromo-substituted dipyrrolylbenzene.…”

Dibenzodiazapyracylenes: Doubly N‐Doped Cyclopenta‐Fused Polycyclic Molecules That Exhibit High Carrier Mobility

“…[10,11] In the series of hetero[8]circulenes, the susceptible electronic properties involving the possible contribution of the central 8π cyclooctatetraene have been investigated from both experimental and theoretical viewpoints. [10,12] Serendipitously, during our investigation on the synthesis of various substituted aza-[8]circulenes, [13] we discovered a synthetic route toward obtaining novel doubly nitrogen-doped pyracylenes. The ortho-phenylene-bridged cyclic tetrapyrroles like 3 a, is usually obtained by Suzuki-coupling reaction of α,α'-diborylated dipyrrole 7 with 1,2-dibromobenzene in a standard concentration (ca.…”

“…In contrast, a hydroxide is attached at the α-position of 9, which may derive from moisture in the air. In both 8 and 9, two sp 3 carbons were detected in their 13 C NMR spectra (Figures S3-14 and S3-16). Difluoro derivative 5 b was also converted to 6 b under the same conditions with a slightly lower yield (6 %).…”

Non-Planar Polycyclic Aromatic Molecules Including Heterole Units

“…Recently, an improved synthetic method has been developed to access to tetraaza [8]circulenes 171a-c bearing substituents at the benzo scaffolds using commercially available 1,2-dibromobenzene derivatives. 79 Tetraaza [8]circulenes 171a-c shows perturbed electronic properties depending on the substituents.…”