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A method for the preparation of an α-formylated pyrrole or dipyrromethane which contains an electron-withdrawing β-acetyl is described. Formylation proceeds directly from the corresponding acid pyrrole or dipyrromethane without the need of the usual two-step acid decarboxylation/formylation procedure. The acid is first transformed into its acid chloride with oxalyl chloride, followed by reduction to the aldehyde with the mild reducing agent sodium triacetoxyborohydride, in a one-pot reaction. The non-basic acylating reagent PR₃ is necessary both for acyl chloride formation and for the reduction to succeed.

The condensation of pyrrole and benzaldehyde has generally been carried out with trifluoroacetic acid (TFA)(20-50 mM), BF₃-etherate (1 mM), or more recently with BF₃-etherate in the presence of a salt. Differences in the reaction course with TFA or BF₃-etherate prompted studies of the combined use of BF₃-etherate and TFA. We found that the reaction of pyrrole + benzaldehyde (10 mM each) cocatalyzed by TFA (15 mM) and BF₃-etherate (0.3 mM) provided tetraphenylporphyrin (TPP) in yields of 50–55%, compared with 40% or 26%, respectively, from optimal catalysis by TFA (20 mM) or BF₃-etherate (1 mM) individually. Examination of the oligomer composition (LD-MS), yield of TPP (UV-vis), yield of N-confused TPP (HPLC), and level of unreacted aldehyde (TLC) in the cocatalytic reaction indicated a reaction course that contained features of those observed with each acid individually. Cocatalysis also was observed with methanol (50 mM) and BF₃-etherate (1.0 mM), which gave TPP in ~40% yield. The beneficial effect of an added salt in BF₃-etherate catalyzed reactions was reexamined by comparisons of reactions with NaCl/BF₃-etherate versus BF₃-etherate alone in terms of the oligomer composition, yield of TPP, yield of N-confused TPP, level of unreacted aldehyde, reversibility of the reaction, inactivation of the acid, and formation of TPP via intermediate oligomers. The studies strongly suggest that the presence of salt facilitates the addition of benzaldehyde to pyrrolic units (which is the limiting step with catalysis by BF₃-etherate alone), thereby affording better utilization of the aldehyde and a giving a commensurate increase in the yield of TPP.

The mastery of the optoelectronic properties of conjugated copolymers by substituting their radicals is a promising way for increasing the light absorption and charge career transport in the organic devices active layer. In this paper, we present the chemical synthesis of four different conjugated benzaldehyde derivatives and pyrrole-based copolymers (P–P:B) followed by their conception in thin films on glass substrates by dip coating root from a solution in dichloromethane. UV–Vis measurements showed absorption in good part of the visible region, with an optical gap around 2 eV. Morphological properties observed by scanning electron microscope of the four P–P:B based thin films illustrated homogenous and continuous surfaces with roughness and surface shape that can be modulated according to Nitrobenzylidene derivative that contains the copolymer. First oxidation ($E_p$) and reduction ($E_n$) potentials of synthetized copolymers have been estimated by cyclic voltammetry which led us to estimate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. The HOMO and LUMO energy level diagram of P–P:B compared with the most commonly used organic materials as donor/acceptor couples showed a cascade shape, which allowed us to opt for organic solar cells based on multiple active layers in our aim to improve its performance.

Condensation of pyrrole and 3,5-di-tert-butyl-2,6-dinitrobenzaldehyde in CH₂Cl₂ in the presence of BF₃·Et₂O affords 5,10,15,20-tetrakis-(2',6'-dinitro-3',5'-di-tert-butylphenyl)porphyrin that can be easily metallated with Zn and Fe.

Metalation of 5,10,15,20-tetrakis-(2',6'-diacrylamido-4'-tert-butylphenyl)porphyrin with Zn(OAc)₂·2H₂O afforded the expected Zn derivative whose X-ray crystal structure reveals a Zn atom hexacoordinated by the four pyrrolic nitrogen atoms and two molecules of H₂O.

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M(TPhPyrPc), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn^III(TPhPyrPc^-2) and that the reduction of Mn^II(TPhPyrPc^-2) to be centred on the ring and rather than on the metal, forming the Mn^II(TPhPyrPc^-4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

5,15-substituted porphyrins are valuable compounds in bioorganic and materials chemistry. A new synthesis has been developed that employs 1,9-diformylation of a dipyrromethane, conversion of the diformyldipyrromethane to the bis(imino) derivative, and reaction of the bis(imino)dipyrromethane + a dipyrromethane to give the zinc-porphyrin bearing trans-AB-substituents. 1,9-diformylation was achieved via Vilsmeier reaction. Imination was achieved by treatment of the 1,9-diformyldipyrromethane with excess amine under neat conditions at room temperature. The porphyrin-forming reaction was carried out over 2 h in refluxing ethanol containing zinc acetate exposed to air. Oxidation of the intermediate porphyrinogen occurs aerobically. A complex composed of two bis(imino)dipyrromethanes and two zinc atoms was observed to form reversibly during the course of the reaction. A set of zinc-porphyrins with trans-AB-, A₂-, or A-substituents has been prepared in yields of ~30% (without detectable scrambling) with straightforward purification. The reaction is applicable to A/B substituent combinations of aryl/aryl, aryl/alkyl, and aryl/H.

Synthetic routes to mono- and di-carboranylpyrroles (1-5) bearing the carborane groups linked either directly to the 3- and/or 4-positions of the pyrrole ring or via one or two methylene spacers are described. Several X-ray structures of key intermediates are presented and discussed. Carboranylpyrroles can be cyclotetramerized to afford carboranylporphyrins in low to moderate yields, depending on the number of carborane cages and their linkage to the pyrrole ring. The best yields of porphyrin were obtained with pyrrole 3, bearing a two carbon spacer between the carborane and pyrrole units. The electrochemical polymerization of pyrroles 2 and 3 gave functionalized conducting polymer films with increased overoxidation resistance and thermal stability compared with unsubstituted polypyrrole. Dicarboranylpyrrole 4 did not electropolymerize under a variety of experimental conditions, whereas pyrrole 5 formed only soluble oligomers.

Unsubstituted porphycene was prepared in 65% yield from 2,7,12,17-tetra-tert-butylporphycene. Taking into account the yield of the substrate, this represents more than a five-fold improvement compared to the methodology used to date. Enhanced availability of the parent porphycene may be exploited in synthetic procedures based on derivatization of the unsubstituted compound.

The Thompson group aims to further the chemistry of pyrroles, dipyrrins and prodigiosenes. This micro-review discusses each of these research areas in turn, focussing on our achievements thus far.

Novel palladium(II) complexes with α,α'-bis(phenylimino)- and α,α'-bis(picolyl)-substituted meso-H-dipyrromethanes have been prepared. The complexes are able to react with dioxygen upon activation with potassium tert-butoxide. Reactions with dioxygen afford C-N or C-C self-bond cleavage producing α-pyrrole-carboxylate or α-hydroxypyrrole residues, respectively. According to DFT calculations the deprotonation of meso-hydrogen leads to the redistribution of electron density between ligand and metal, thus formally forming dipyrromethene-palladium(0) anionic complex. Possible reactive oxygen-containing intermediates have been suggested on the basis of calculations.

Calix[4]pyrroles have attracted considerable attention within the macrocyclic, supramolecular, and porphyrin analog communities due to their ability to act as simple-to-synthesize receptors for common anions, such as chloride and fluoride. Reported here is what we believe is a new, potentially generalizable route to fully β-alkyl substituted calixpyrroles. These products are accessible from the starting pyrrolic esters, and are obtained via simple reaction with CH₃Li, followed by subsequent quenching with HCl in ether. A representative system has been characterized by X-ray diffraction analysis. The present route allows access to calix[4]pyrroles bearing functionality, such as double bonds, off the so-called C-rim; such systems are of interest because they could allow for further synthetic elaborations and permit incorporation of calix[4]pyrroles into more complex structures.

Combinatorial libraries of substituted tetrapyrrole macrocycles, which can now be prepared via a variety of approaches, typically are rich in isomers. Terminology for describing such isomers (due to distinct patterns of peripheral substituents) is delineated in several illustrative examples. A hierarchical relationship exists of molecular formula, condensed formula(s) of substituents, set(s) of pyrrole collocates (conveying each pair of β-pyrrolic substituents), and isomers of substituted tetrapyrrole macrocycles. Isomers with identical pyrrole collocate sets can arise owing to distinct positions or orientations of the (homo- or hetero-substituted) pyrrolic units in a macrocycle. Consideration of a handful of virtual combinatorial libraries illustrates tradeoffs of library size, chemical richness, and isomeric content. As one example, octa-derivatization of a tetrapyrrole scaffold with eight reactants A–H affords 2,099,728 members (99.7% isomers, 82,251 pyrrole collocate sets, and 6,435 condensed formulas) whereas the reversible self-condensation of four pyrroles that bear the same eight entities (AB, CD, EF, GH) affords 538 members (93.5% isomers, 35 pyrrole collocate sets, and 35 condensed formulas). Derivatization affords all combinations and permutations whereas self-condensation of substituted pyrroles carries collocational restrictions. Understanding such tradeoffs and the structural origin of isomerism are important aspects in the design of tetrapyrrole combinatorial libraries.

A new methodology for the synthesis of a new series of mesotetrakis[aryl]-21H,23H-porphyrin derivatives 5a–5d, 6a–6c, 7 and 8 is presented. Structures of new compounds were established based on both elemental and spectral data. Cytotoxicity activity of the newly synthesized compounds was investigated against two human cell lines MCF-7 and HepG2. Molecular docking was performed to investigate the binding between the most active porphyrin derivatives and Bcl-2 molecular biomarkers in HepG2 cells.

Three series of pyrrole-contained fused ring compounds are summarized. In recent years, these compounds attracted wide attention with their special and elegant structures. Furthermore, they have played important roles in new optoelectronic materials and guest receptors due to their excellent photoelectric effects and unique properties with nitrogen atom doping.

Bacteriochlorins – Nature’s near-infrared (NIR) chromophores – are distinguished by an intense ($𝜀$ ∼;10⁵ M${}^{-1}$cm${}^{-1})$ long-wavelength absorption band in the ∼;700–1000 nm. The development of routes to prepare synthetic, tailorable bacteriochlorins holds promise for multiple disciplines where NIR-light-promoted photoactivity is of interest. A de novo route to bacteriochlorins equipped with a stabilizing gem-dimethyl group in each pyrroline ring was discovered in 2003. Continued development in this arena over 20 years has led to additional routes as well as methods to install substituents at selected positions about the perimeter of the macrocycle. The present paper reports studies that highlight substantial limitations of existing synthetic routes, including stymied access to multi-bacteriochlorin arrays and the inability to install (in a rational way) distinct groups at opposite sides of the macrocycle. The origins of the limitations are traced to particular stages of the chemistry ranging from derivatizing pyrroles, creating pyrrolines, constructing and elaborating dihydrodipyrrins, coupling dihydrodipyrrins, and forming macrocycles. Through exploration of a dozen aspects of bacteriochlorin syntheses, 60 new compounds (and nine known compounds via improved syntheses) have been prepared and characterized; the data include 20 single-crystal X-ray diffraction analyses. The research taken together points to areas of focus to fulfill the promise of this fascinating class of compounds.

A simple pyrrole-based Schiff base ligand, 2-[(2-pyrrolylmethylene)amino]phenol was used to synthesize a unique tetra palladium(II) complex by treating it with PdCl₂ in CH₃OH/CH₃CN for 1 h at room temperature. X-ray structure showed that each Pd(II) ion adopted a distorted square pyramidal structure and bonded to pyrrole “N”, imine “N”, two phenolate “O”s, and one Pd(II) ion with direct Pd(II)-Pd(II) bond. Three ligands are involved in completing the square pyramidal geometry of each Pd(II) ion and the structure appeared as a hashtag symbol and four Pd(II) ions formed a plus symbol within the hashtag structure. The tetra palladium (II) complex showed a very simple NMR spectrum and absorbs strongly in the UV-visible region.

Man has always used his environment to heal himself. Until 1869 all medicines came mainly from plants (e.g. opium for pain relief, Figure 8.46, Section 8.8.1) or animals (e.g. badger skin and meat to relieve snake or scorpion bites). In 2010, there were 1000 active ingredients in drugs sold in pharmacies, of which 10% were unmodified natural products, 29% were derivatives of natural products (hemisynthesis) and 61% were synthetic products. Using bio-informatics and artificial intelligence methods, an estimated 166 billion different molecules can be prepared by combining 17 atoms comprising C, N, O, S, F, Cl, Br and I, and by applying known synthesis methods and standard stability criteria. By applying medicinal chemistry criteria (structure/biological activity relationships) to this molecular space called GBD17, it is estimated that 10 million of these molecules could become drugs…