Light-responsive rotaxane-based materials: inducing motion in the solid state

• Adrian Saura-Sanmartin

Beilstein J. Org. Chem. 2023, 19, 873–880, doi:10.3762/bjoc.19.64

• direction, one potential strategy is the approach followed by Feringa and co-workers [72], in which palladium-porphyrin photosensitizer-based struts were employed within a metal-organic material, allowing the use of green light as irradiation source because of the effective energy transfer between these

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• transition metal (Ni, Fe, V) porphyrin catalysts and oxygen. Catalytic reduction (H2, Pd/C) affords 2,2'-diaminobibenzyl (20) in the subsequent step [28]. 1.2 Ring-closing via amine condensation The initial synthesis of 10,11-dihydro-5H-dibenzo[b,f]azepine (2a) was reported in 1899 by Thiele and Holzinger

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

• Semyon V. Tsybulin,
• Ekaterina A. Filatova,
• Alexander F. Pozharskii,
• Valery A. Ozeryanskii and
• Anna V. Gulevskaya

Beilstein J. Org. Chem. 2023, 19, 674–686, doi:10.3762/bjoc.19.49

• singlet oxygen production have been identified in porphyrin-based butadiynes [7][8][9], 1,3-butadiyne-linked oligoporphycenes [10], and 1,3-butadiyne-linked amines [13]. A wide variety of applications was proposed for graphdiynes (2D allotropes of graphene), including electrocatalysts and energy devices

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• connect two diverse moieties in a single framework. Therefore, this review focuses on the synthesis and photophysical studies of β- and meso-substituted and 1,2,3-triazole-fused porphyrin conjugates. All of the porphyrin conjugates discussed here are synthesized via a copper(I)-catalyzed Huisgen 1,3

• -dipolar cycloaddition reaction between an azide and a terminal alkyne, also popular as "click reaction" or CuAAC reaction. Moreover, the 1,2,3-triazole ring also serves as a spacer and an electron transfer bridge between the porphyrin and the attached chromophores. In order to provide a critical overview

• of the synthesis and properties of various porphyrin-triazole hybrids, this review will discuss some of the key reactions involved in the preparation of triazole-linked porphyrin conjugates. Keywords: azide–alkyne; click chemistry; CuAAC; 1,3-dipolar cycloaddition; porphyrin; 1,2,3-triazole

Synthesis of meso-pyrrole-substituted corroles by condensation of 1,9-diformyldipyrromethanes with pyrrole

• Baris Temelli and
• Pinar Kapci

Beilstein J. Org. Chem. 2022, 18, 1403–1409, doi:10.3762/bjoc.18.145

• studies on porphyrins, which have many application areas such as photodynamic therapy and photovoltaic systems, have focused on oligomeric and polymeric structures in the last two decades [5][6][7][8][9]. Although such porphyrin structures have been used successfully in the development of molecular

• our knowledge, there is no generally accepted method for the synthesis of pyrrole-substituted corroles. Very recently, we reported the synthesis of porphyrin–corrole [24][25][26] and porphyrin–porphyrin dyads and triads [27] using formylated porphyrin compounds. In a continuation of research activity

• . Figure 2 shows the absorption spectrum of 2a with a strong Soret band at 412 nm and weak Q-bands at 542 and 611 nm. After the synthesis of corrole compounds, we tried to extent our studies to obtain meso-pyrrole-substituted porphyrin compounds. For this purpose, the MacDonald [2 + 2] porphyrin

Cytochrome P450 monooxygenase-mediated tailoring of triterpenoids and steroids in plants

• Karan Malhotra and
• Jakob Franke

Beilstein J. Org. Chem. 2022, 18, 1289–1310, doi:10.3762/bjoc.18.135

• system as well as a cysteine thiolate ligand from the protein backbone (Figure 1B). The generally accepted catalytic cycle for hydroxylations is shown in Figure 1C. In the resting state A, the central ferric ion is coordinated by six ligands, four from the porphyrin ring system, one cysteine thiolate

• group and an aqua ligand (water), resulting in an octahedral complex [17]. The oxidative reaction is initiated by displacement of the axial water molecule by the substrate (step 1), which pushes the Fe(III) ion out of the porphyrin plane in intermediate B [17]. This geometrical distortion promotes

• compound I (intermediate G), it is now generally accepted as a ferryl (Fe(IV)) oxo species with a radical cation in the porphyrin system [18][23]. In the case of hydroxylations, the oxygen from compound I (intermediate G) can then be transferred by an oxygen rebound mechanism (steps 7 and 8) via the ferryl

Scope of tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the synthesis of triazoloquinoxalines, imidazoloquinoxalines, and rhenium complexes thereof

• Laura Holzhauer,
• Chloé Liagre,
• Olaf Fuhr,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2022, 18, 1088–1099, doi:10.3762/bjoc.18.111

• 1,2,3-triazoloquinoxalines 3 and imidazo[1,2-a]quinoxalines 2 under conditions known for copper-catalyzed azide–alkyne cycloaddition (CuAAC) [10]. The currently published porphyrin-catalyzed process requires glovebox conditions and the use of an expensive catalyst [11]. We intend to elucidate the

• ). Improving this route provides an alternative to the literature-known method [11] that requires both a special porphyrin complex and glovebox conditions. Using neither silver(I) triflate nor copper(I) iodide yielded the imidazole product, indicating that the use of copper(I) triflate is crucial for the

• ]). Reactions of tetrazoloquinoxalines 1 to 1,2,3-triazoloquinoxalines 3 via CuAAC and denitrogenative annulation to imidazo[1,2-a]quinoxalines 2 catalyzed by an iron porphyrin catalyst 5 in combination with Zn. The scheme includes all quinoxaline-based derivatives that were obtained by these procedures so far

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• demonstrated by Reek and co-workers by using a previously reported heteroleptic bisporphyrin cage [76]. The tetragonal prismatic nanocage 47 consisted of two zinc-porphyrin units along the two tetragonal faces (Figure 11), which allowed encapsulation of the chiral phosphoramidite 48 as a precursor for the

• + was developed on the basis of two complexation events, i.e., the zinc(II) HETTAP (log β = 14, log K1 ≥ 6) and Npy → ZnPor (log K = 4.45) binding motifs (Figure 12) [89]. Due to the design of 52, the pyridine terminal oscillates between the two degenerate zinc porphyrin (ZnPor) stations of 53 at k298

• able to build a new catalytic machinery [100]. Hereunto, the two concepts RPI and ILC were combined in a synergistic manner, starting with rotor [Cu2(83)(91)]2+ (k298 = 46.0 kHz) that catalyzed the click reaction between the zinc porphyrin ligand 92 and the azide 93 furnishing triazole 94 (Figure 20

Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• substrate 26 was first modified at the hydroxy groups through esterification with a designed acid moiety possessing a p-tert-butylphenyl group and transformed to the corresponding model substrate 27. The catalyst H used here was a manganese(III)-bounded porphyrin module carrying four β-cyclodextrin units at

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• inspired by the biocatalytic action of the cytochrome P-450 cycle, which is driven by a reductase or bioreductant, and presented high versatility in incorporating both aldehyde and ketone functionalities into unprotected arylboronic acids. The reaction consists of using a porphyrin-based iron catalyst, and

• muscarinic acetylcholine receptor agonists (97, 98, and 99, Scheme 33A) [168]. Asymmetric variations of the porphyrin-based iron catalysts also provided the desired product with 100% conversion and enantiomeric ratios up to 73:27 in some cases. The straightforward Fe catalysis was used as a key step in the

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• late-stage fluorination (Csp3–F) is relatively challenging due to the omnipresent unactivated C–H bonds of the substrate molecules. In 2012, Groves et al. revealed a manganese porphyrin-catalyzed late-stage Csp3–H fluorination method (Scheme 1) [22]. In the authors’ approach, a direct late-stage

• [24]. This manganese porphyrin catalytic system was also effective in the direct site-selective fluorination of complex steroid scaffold 3, containing 28 unactivated C–H bonds. Based on the authors’ analysis of steric and electronic factors, it was suggested that the methylene units at C2 and C3 of

• future, such as protecting-group-free methodologies, peptide biosensors, and facile functionalizations within unexplored realms of complex peptides. Proposed reaction mechanism of C–H fluorination by a manganese porphyrin catalyst. Proposed mechanism of C–H radiofluorination. Proposed reaction mechanism

Structural effects of meso-halogenation on porphyrins

• Keith J. Flanagan,
• Maximilian Paradiz Dominguez,
• Zoi Melissari,
• Hans-Georg Eckhardt,
• René M. Williams,
• Dáire Gibbons,
• Caroline Prior,
• Gemma M. Locke,
• Alina Meindl,
• Aoife A. Ryan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2021, 17, 1149–1170, doi:10.3762/bjoc.17.88

• , Trinity College Dublin, The University of Dublin, Dublin 2, Ireland Van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands 10.3762/bjoc.17.88 Abstract The use of halogens in the crystal engineering of supramolecular porphyrin assemblies

• we were able to deduce the impact a meso halogen has on a porphyrin, for example, meso-halogenation is dependent on the type of alternate substituents present when forming supramolecular assemblies. Furthermore, we have designed a method to predict the conformation of halogenated porphyrins, without

• few decades. Byrn et al. were the first to observe that porphyrins have a high propensity to form “porous” clathrates and suggested that they can be used as a “porphyrin sponge” [1]. They reported that 5,10,15,20-tetraphenylporphyrin could act like a ‘host’ which could trap a variety of solvent

Manganese/bipyridine-catalyzed non-directed C(sp³)–H bromination using NBS and TMSN₃

• Kumar Sneh,
• Takeru Torigoe and
• Yoichiro Kuninobu

Beilstein J. Org. Chem. 2021, 17, 885–890, doi:10.3762/bjoc.17.74

• reported the manganese-porphyrin-catalyzed chlorination and bromination of C(sp3)−H bonds, respectively (Scheme 1d). Groves et al. also reported the manganese-salen-catalyzed fluorination of benzylic C(sp3)−H bonds [49]. Although these methods are efficient, they have a limited substrate scope

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• + and crown ether, leading to the formation of cyclobutane in a high yield. D’Souza et al. constructed a photosynthetic triad 4 to mimic the photosynthetic reaction center [19]. A BODIPY, an ammonium-functionalized fullerene, and a zinc porphyrin functioned as the energy donor, electron acceptor, and

• electron donor, respectively (Figure 3). A benzo-18-crown-6 derivative was connected to the porphyrin ring, which could form a supramolecular complex with fullerene through dipole interactions. The formed supramolecular self-assembly resulted in a high energy-transmission efficiency (over 97%) between the

• BODIPY and the zinc porphyrin. The excited zinc porphyrin further transferred the electron to the fullerene, yielding a charge-separated state, with a long lifetime of 23 µs, indicating the charge stabilization of the supramolecular assembly. Thus, an artificial photocatalytic system that can mimic the

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• self-sorting protocols. The present mini review will provide an overview over the latest advancements in this field with a focus on reversibly switchable functions in discrete supramolecular systems. Keywords: copper; fluorescence; self-assembly; self-sorting; zinc porphyrin; Introduction Since self

• )] (Figure 4e). Equally, Schalley and Nitschke developed a guest-induced self-sorting based on two new Zn4L6 cages (Figure 5a) using the aldehyde 9 and the diamine subcomponents 7 and 8 that contained either the naphthalene diimide or zinc porphyrin moiety [51]. Both cages respond selectively to distinct

• chemical stimuli yielding different supramolecular products. The porphyrin ligands of the cage [Zn4(8')6]8+ interacted favorably with C70 as a guest, whereas an electron-rich aromatic crown-ether did thread onto the electron-deficient naphthalene diimides of cage [Zn4(7')6]8+ forming mechanically

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• ], switchable NMR relaxation agents [8][9][10], and building blocks for molecular spintroncis [11]. Our modular design is based on three components: a) a Ni(II)-porphyrin (square planar base complex), b) an azoaryl unit (photoswitchable ligand) and c) a molecular linker or tether (connecting the porphyrin with

• the switchable ligand). This approach has been dubbed “record player” design for obvious reasons (Figure 1a). The Ni-porphyrin (“disk”) is low-spin if the azo-aryl unit (“tone arm”) is in trans configuration. Upon switching to the bent cis configuration, the lone pair of the pyridine (or imidazole

• components (Ni-porphyrin, azo-aryl unit, and tether) have to be carefully designed and tuned regarding their geometry and electronic properties. The Ni-porphyrin should be electron deficient (electron-withdrawing substituents in meso position), the azo-aryl unit should be electron rich (electron-donating

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• amino substituents can be attached [52][53][54][55][56][57][58][59][60]. Several porphyrin ligands show tight (nM) binding and can cause unfolding of the targeted protein [52][53][54][55]. However, other porphyrin ligands were used to recognize protein surfaces in a native state [56][57], promoted

• indeed recognize the highly positively charged area on cytochrome c (Cyt c) that binds Cyt c peroxidase. The inhibition of this protein–protein interaction was demonstrated as well using a luminescence quenching assay. The protein surface recognition of two porphyrin ligands bearing carboxylate

• docking that the Cyt c/porphyrin complexes exist as a dynamic ensemble where multiple surface patches can transiently interact with the ligand through a combination of hydrophobic interactions with the porphyrin core and electrostatic interactions with the carboxylate substituents. Cucurbit[7]uril and

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• Abstract We present the synthesis and the photochemical and catalytic switching properties of an azopyridine as a photoswitchable ligand, covalently attached to a Ni(II)-porphyrin. Upon irradiation with 530 nm (green light), the azopyridine switches to the cis configuration and coordinates with the Ni2

• -epoxypropane to propylene carbonate using an aluminum porphyrin and a photoresponsive ligand. The catalytic activity of the metal porphyrin depended on the axial coordination of an azostilbene and coordination of the latter ligand was controlled by photoisomerization of the stilbene unit [9]. Hecht et al

• by coordination/decoordination to the Ni2+ ion in a Ni-porphyrin. So-called record player molecules, including a Ni(II)-porphyrin as the square planar base complex and azopyridines as photoswitchable axial ligands, were previously investigated for spin switching applications [13][14][15][16][17][18

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• postsynthetic modifications in flow [63]. Poliakoff, George, and co-workers reported a porphyrin photosensitiser ionically immobilised to sulphonate-cross-linked ion exchange polystyrene resins (amberlyst-15) for the synthesis of artemisinin (49). This resulted in a bifunctional material, which acts as a HPCat

• and heterogeneous Brønsted acid catalyst, which are both required for independent steps in the synthesis [132]. They suggested that the porphyrin was protonated by the amberlyst-15 sulphonate groups and immobilised to the solid surface by electrostatic forces, rationalising the observed change in

• porphyrin colour from a purple powder to green when immobilised. The immobilisation of porphyrins onto polystyrene supports has been reported prior to this through covalent and electrostatic attractions but often suffered from poor coupling yields and low loadings [133][134][135][136]. Similarly, ionic

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• porphyrin [75] and rhodamine 6G (OD14) [76]. Aryl radicals from aryl halides. Aryl halides are generally more difficult to reduce than aryl diazonium salts (Ered < −1.2 V) [77][78]. However, they are more available and bench-stable. Their reduction potential is dependent on the substitution pattern and on

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• , 68502-100, Brazil 10.3762/bjoc.16.83 Abstract In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly

• renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors’ opinion. Keywords: energy transfer; photocatalysis; photooxygenation; photoredox; porphyrins; Introduction In

• continuous-flow photochemistry a sustainable alternative approach being applied already by the chemical and pharmaceutical industries. Porphyrinoid is the term given for a class of organic compounds containing four pyrrole rings connected by four methylene bridges, and include porphyrin, chlorin

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• investigated for its use as a rigid isolating unit in the synthesis of multichromophoric arrays. Sonogashira cross-coupling conditions are utilized to attach various porphyrins and boron dipyrromethenes (BODIPYs) to the triptycene scaffold. While there are previous examples of triptycene porphyrin complexes

• , this work reports the first example of a linearly connected porphyrin dimer, linked through the bridgehead carbons of triptycene. Symmetric and unsymmetric examples of these complexes are demonstrated and single crystal X-ray analysis of an unsymmetrically substituted porphyrin dimer highlights the

• porphyrin units have been connected in a number of different ways; from phenylene, ethynyl, ethenyl or alkane linkers [5][6][7][8], to meso–β- [9] or β–β-linkages [10] or alternatively by connecting two or more meso–meso-linked porphyrin units via oxidative fusing reactions [11][12][13][14][15]. However

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• prepared based on the reaction of Zn(II) or Ni(II) complexes of 5,10,15,20-tetrakis(4-amino-2,3,5,6-tetrafluorophenyl)porphyrin and chlorin with maleic anhydride. Porphyrin maleimide derivatives were also prepared by the reaction of 5,10,15,20-tetrakis(4-azido-2,3,5,6-tetrafluorophenyl)porphyrinato Zn(II

• ) or Ni(II) with N-propargylmaleimide via the CuAAC click reaction to afford fluorinated porphyrin–triazole–maleimide conjugates. New maleimide derivatives were isolated in reasonable yields and identified by UV–vis, 1H NMR, 19F NMR spectroscopy and mass-spectrometry. Keywords: chlorin; maleimide

• ; porphyrin; spectral characteristics; synthesis; Introduction Porphyrins belong to a broad class of the natural and synthetic macroheterocyclic compounds with unique properties. They play an important role in photosynthesis [1], catalysis [2][3], nonlinear optics [4][5], polymer synthesis [6] and energy

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• Groves [82] developed two manganese catalysts for the fluorination of C(sp3)–H bonds (Scheme 38). On the one hand, they employed a manganese porphyrin to catalyze the oxidative aliphatic C–H fluorination with iodosylbenzene (PhIO) as a stoichiometric oxidant. A variety of substrates, including simple