2,2'-Bipyrrole-Based Porphyrinoids

Gram-Scale Synthesis of a Bench-Stable 5,5″-Unsubstituted Terpyrrole

The controlled preparation of higher order oligopyrrolic species holds broad utility across the chemical and material sciences. Here, we describe the gram-scale synthesis of a bench-stable 5,5″-unsubstituted terpyrrole in excellent yield via a tandem Suzuki cross-coupling with in situ deprotection. The solution and solid-state stability as well as UV-vis, fluorescence, and single crystal X-ray diffraction structure are also detailed.

Cu-Catalyzed Tandem Aerobic Oxidative Cyclization for the Synthesis of 3,3'-Bipyrroles from the Homopropargylic Amines

A Cu-catalyzed method for the synthesis of 3,3'-bipyrroles from homopropargylic amines through tandem aerobic oxidative cyclization involving the formation of C-C bond has been developed. The features of this reaction are a small number of Cu catalysis and simple starting substrates. Moreover, this procedure exhibits good functional group tolerance and a series of 3,3'-bipyrroles derivatives are obtained in moderate to good yields.

Functionalized 2,2'-Bipyrroles: Building Blocks for Pyrrolic Macrocycles

Functionalized N-unsubstituted 2,2'-bipyrroles are basic building blocks for the preparation of pyrrolic macrocycles and natural products, such as prodigiosines. The aim of this review is to provide a description of the most important methodologies used to prepare 2,2'-bipyrroles and their central role as building blocks for the synthesis of porphyrinoids and property-defining structural elements therein.

Supramolecular Chemistry of Anionic Dimers, Trimers, Tetramers and Clusters

Two or more anions constrained in close proximity within a single pocket are found in a number of natural systems but a less common motif in artificial systems. This review summarizes work on anion receptors capable of stabilizing anionic dimers, trimers, tetramers and clusters in a well-defined fashion. These systems may provide insights into the fundamental chemistry of anion-anion interactions and provide a guide for understanding in greater detail a number of biological and environmental processes, as well as key tenants of relevance to supramolecular chemistry, extraction, transport, crystal engineering, and the like. The primary goal of this review is to provide a general introduction into multi-anion recognition chemistry for the benefit of supramolecular and non-supramolecular chemists alike.

An Acid-Responsive Single Trichromatic Luminescent Dye That Provides Pure White-Light Emission

A novel acid‐responsive single trichromatic luminescent dye capable of emitting pure white light (WL) is reported. A newly designed p‐phenylene‐bridged bipyrrole bearing N‐alkylimino groups (1 a) specifically provides WL emission upon mixing with trifluoroacetic acid (TFA) in a CH₂Cl₂ solution. The emission originates from the trichromatic luminescent behavior of 1 a upon protonation of the imino groups. The blue‐light‐emitting 1 a exhibits dramatic color changes in fluorescence to orange and green upon mono‐ and diprotonation, respectively, providing a wide emission band in the range of λ=400–800 nm that provide WL when the compound is in a dynamic equilibrium between the three states. The sample also exhibits low self‐absorption of the emitted light and a high fluorescence quantum yield upon excitation with UV light.

Heterocorrole Conformations: Little Saddling, Much Ruffling

10-Heterocorrole complexes with oxygen, sulfur, and selenium at position 10 of the macrocycle and with the divalent ions of nickel, copper, and palladium were prepared and investigated. The focus was set on the size adaptation and matching mechanisms of cavity size versus ionic radius in corrole-type macrocycles. A full set of single-crystal X-ray analytical data revealed that in all but one case the N₄ binding site of the ring-contracted tetrapyrrole was larger than necessary to bind the metal ion without deformation. In-plane size adaptation through M-N bond-length elongation by 2.5-3.2 % was effective, as well as pronounced out-of-plane ruffling of the macrocycle for those compounds with a more severe size mismatch. Such ruffling had been excluded for corroles previously, but is apparently the most efficient mechanism to adapt to small central ions.

Stable 5,5'-Substituted 2,2'-Bipyrroles: Building Blocks for Macrocyclic and Materials Chemistry

The preparation and characterization of a family of stable 2,2'-bipyrroles substituted at positions 5 and 5' with thienyl, phenyl, TMS-ethynyl, and vinyl groups is reported herein. The synthesis of these new bipyrroles comprises three steps: formation of the corresponding 5,5'-unsubstituted bipyrrole, bromination, and Stille or Suzuki coupling. The best results in the coupling are obtained using the Stille reaction under microwave irradiation. The new compounds have been fully characterized by UV-vis absorption, fluorescence, and IR spectroscopies and cyclic voltammetry. X-ray single-crystal analysis of four of the synthesized bipyrroles indicates a trans coplanar geometry of the pyrrole rings. Furthermore, the substituents at positions 5,5' remain coplanar to the central rings. This particular geometry extends the π-conjugation of the systems, which is in agreement with a red-shifting observed for the λ_max of the substituted molecules compared to the unsubstituted bipyrrole. All of these new compounds display a moderate fluorescence. In contrast with unsubstituted bipyrroles, these bipyrroles are endowed with a high chemical and thermal stability and solubility in organic solvents.

Pyrrole N-H Anion Complexes

Synthetic pyrrole-based anion receptors date back to the 1990s. They have been extensively developed in the context of macrocyclic systems as expanded porphyrins and calixpyrroles, and related systems. The chemistry of open-chain pyrrolic systems is, in many respects, no less venerable. It also has more direct analogy to naturally occurring pyrrole-based anion binding motifs. However, it has not been the subject of a comprehensive review. Presented herein is a summary of efforts devoted to the creation of de novo pyrrole-based receptors, as well as the anion recognition chemistry of naturally occurring pyrrolic systems as prodigiosins and their synthetic analogues.

Facile Generation of A2B Corrole Radical Using Fe(III) Salts and Its Spectroscopic Properties

A carboxyphenyl-substituted corrole, 5,15-dimesityl-10-(4'-carboxyphenyl)corrole (1), has been synthesized and characterized by UV-vis, fluorescence, ¹H NMR spectroscopy, and electrospray ionization (ESI)-mass spectrometry (MS) techniques. An air-stable corrole radical (1^•) was obtained with the addition of the Fe(III) salt to 1 in dimethyl sulfoxide (DMSO) and characterized by UV-vis, fluorescence, electron paramagnetic resonance (EPR), ESI-MS techniques, and density functional theory studies. The neutral corrole radical (1^•) exhibited a sharp EPR signal at g = 2.006 in DMSO. The reduced bipyrrolic (N-C-C-N) dihedral angle (χ) of 1 from 19.11 to 7.07° leads to the release of angle strain, which is the driving force for the generation of 1^•. Notably, trans-dimesityl groups prevent the dimerization or aggregation of the corrole radical. Further, 1^• was converted to 1 by excess addition of Fe(II) salts in DMSO at 298 K.

The first synthesis of meso-dicycloalkylporphycenes: ring strain effects on structural and optical properties of isomeric porphyrins

Two novel meso-dicycloalkylporphycenes were synthesized for the first time, which showed remarkable ring-strain-induced switching of their fluorescence behaviors in the solution phase.

Total Synthesis and Biological Evaluation of Hybrubin A

Here, we report the first total synthesis of hybrubin A, a bipyrrole tetramic acid alkaloid representing a new carbon framework derived from convergent (truncated red cluster and exogenous hbn cluster) biosynthetic pathways. A highly convergent synthesis was developed, employing 4-methoxy-1,5-dihydro-2H-pyrrol-2-one (13) as a single starting material to provide hybrubin A in three steps from 13 and 20.8% overall yield. As no biological activity was prescribed to hybrubin A except for a lack of cytotoxicity, we further profiled this unique alkaloid across panels of discrete molecular targets. Interestingly, hybrubin A was found to be a ligand for a variety of GPCRs with a propensity for potent binding across therapeutically relevant adenosine receptors (A₁, A_2a, and A₃) as well as a potent activity at a kinase, FLT3. This pattern of biological activity is distinct from other related prodigiosin natural and unnatural products and is even more intriguing in the absence of cytotoxicity.