Efficacy of radical reactions of isocyanides with heteroatom radicals in organic synthesis

• Akiya Ogawa and
• Yuki Yamamoto

Beilstein J. Org. Chem. 2024, 20, 2114–2128, doi:10.3762/bjoc.20.182

• phenanthridines via silver-catalyzed radical sulfonylation–cyclization of 2-isocyanobiphenyls (Scheme 25) [98]. Wang et al. reported a radical borylative cyclization of 2-isocyanobiaryls with N-heterocyclic carbene borane (Scheme 26) [99]. The boryl radical generated via hydrogen abstraction in the presence of di

• -(tert-butylperoxy)-2-methylpropane (DTBP) as the radical initiator attacks isocyanide units, and the subsequent radical cyclization successfully proceeds to form a variety of borylated phenanthridines in moderate to good yields. Although the previous examples described the synthesis of phenanthridines

• isocyanides forms the imidoyl radicals, which undergo intramolecular cyclization and oxidative dehydrogenation to give phenanthridines (Scheme 27) [100]. Conclusion In this Perspective, the addition and cycloaddition reactions of heteroatom radicals with isocyanides have been described in detail and their

Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• [7], quinoxalines [8], naphthalimides [9], phenanthridines [10], cyanines [11], or indoles [12], as well as metal-organic complexes [13], and several others [1][2][4]. In this context, benzoquinolizinium derivatives and resembling polycyclic azoniahetarenes are an established class of DNA-binding

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• -hydroxyphthalimide esters 3, resulting in the efficient synthesis of various 6-alkylated phenanthridines 45 (Scheme 19) [37]. The protocol exhibited a wide substrate scope, excellent tolerance towards functional groups, and mild reaction conditions. Based on the experimental observations and a previous report [6

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

Phenanthridine–pyrene conjugates as fluorescent probes for DNA/RNA and an inactive mutant of dipeptidyl peptidase enzyme

• Josipa Matić,
• Tana Tandarić,
• Marijana Radić Stojković,
• Filip Šupljika,
• Zrinka Karačić,
• Ana Tomašić Paić,
• Lucija Horvat,
• Robert Vianello and
• Lidija-Marija Tumir

Beilstein J. Org. Chem. 2023, 19, 550–565, doi:10.3762/bjoc.19.40

• sensitivity to the polarity of its surroundings. Similar as pyrenes, phenanthridines are also used as fluorescent probes, and their characteristics may be altered by various substituents appended to the aromatic core. The formation of excimers by two or more pyrenes is well known in the literature [4

• luminescence (CPL). The exciplex (excited heterodimer) formed intramolecularly proved to be conformationally rigid and consequently was not sensitive to solvent or temperature [8]. Further, pyrenoimidazole-fused phenanthridines have been reported recently, developed as fluorescence emitters for optoelectronic

• combine to produce an excimer, which is identifiable by a certain fluorescence band [11][12]. Some of the pyrenes and phenanthridines exhibited meaningful biological activity. Several pyrene-guanidiniocarbonylpyrrole derivatives have been found to exhibit the affinity for ds-DNA that is strongly pH

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• exposed to UV radiation affording phenanthridines. The scope and limitations of this novel reaction were explored. For example, exposure of 2',3'-dimethoxy-[1,1'-biphenyl]-2-carbaldehyde O-acetyl oxime to UV radiation afforded 4-methoxyphenanthridine in 54% yield. This methodology was applied to the

• synthesis of trisphaeridine to afford the product in four linear steps in an overall yield of 6.5% from 1-bromo-2,4,5-trimethoxybenzene. Keywords: aromatic compounds; cyclization; iminyl radical; phenanthridines; radical cation; synthesis; UV irradiation; Introduction Phenanthridine derivatives have

• ], rhodium-mediated alkyne [2 + 2 + 2] cycloaddition reactions [3], and the palladium-catalysed aerobic domino Suzuki coupling/Michael addition reaction [4]. The most attractive and common strategies to phenanthridines rely on intramolecular cyclizations of various ortho-functionalized biaryl precursors

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• for the synthesis of perfluoroalkyl-substituted phenanthridines. In 2018, Sundén and Hsu [31] proposed a method of adding an α-aminoalkyl radical to maleimide via an EDA complex based on previous work (Scheme 10). The corresponding products can be given in good yield by modifying substituents on the N

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• ; phenanthridines; photocatalysis; radicals; visible light; Introduction Phenanthrenes are widely investigated compounds, due to the impressive number of diverse applications involving this scaffold, ranging from medicinal chemistry [1] to materials sciences, including their use in optoelectronics [2][3] and in

• particular phenanthridines, are substructures present in a wide range of both natural and synthetic products, including trisphaeridine [12] (that exhibits an anti-HIV-I protease activity) and the antifungal sanguinarine [13]. Some phenantridinium derivatives are known as well, notably fagaronine (a DNA

• derivatives 3.3a–d upon rearomatization. Notably, the process offers a wide substrate scope and the products are obtained with complete regioselectivity [43]. 2 Synthesis of phenanthridines or related azaarenes Under photocatalyzed conditions, phenanthridines are mostly obtained via an intramolecular radical

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• successfully undergo this cyclization (products 115f–h). C-centered radicals generated in a radical 5-exo-trig cyclization of β,γ-unsaturated oximes 116 upon oxidation by the TBAI/TBHP system were trapped by an isonitrile group of 2-arylphenyl isonitriles 117 to synthesize substituted phenanthridines 118

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• N2) which triggers an intramolecular cyclization reaction via a nitrogen-centred radical intermediate to form sulfonylated phenanthridines. The reaction is photocatalyzed by [Ru(bpy)3]Cl2 under irradiation with blue LEDs and proceeds smoothly for a variety of substituted vinyl azides and sulfonyl

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

Catalytic Wittig and aza-Wittig reactions

• Zhiqi Lao and
• Patrick H. Toy

Beilstein J. Org. Chem. 2016, 12, 2577–2587, doi:10.3762/bjoc.12.253

• ]. In this work, biaryl isocyanates 45 could be converted into phenanthridines 46, and aryl isocyanates 47 could be transformed into benzoxazoles 48 directly in refluxing toluene together with the simultaneous release of carbon dioxide. Presumably these reactions proceeded via iminophosphorane

Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

• from aminobiphenyl and arylaldehyde in dichloromethane in the presence of molecular sieves at room temperature. Radical cyclisation in the presence of (tert-butyl)peroxide in chlorobenzene at 140–150 °C for 48 h, yielded the corresponding phenanthridines in moderate yields. The t-BuO• radical

• eliminated the imine-H and formed the imidoyl radical, added to the phenyl ring. The homolytic aromatic substitution was terminated by H-atom abstraction by another t-BuO• radical. Among very few routes targeting the synthesis of 5,6-unsubstituted phenanthridines, the here presented radical-based pathway

• -isocyanobiphenyls with CF3SiMe3 under metal-free conditions showed to be a mild and efficient approach to 6-(trifluoromethyl)phenanthridines, characterised by good yields with high regioselectivity at ambient temperature (Scheme 6) [19][20]. Another radical-based route (targeting 6-perfluoroalkylphenanthridines

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• communicated previously, 3-substituted phenanthridines 10a–f were isolated in good to quantitative yields (52–99%, Scheme 1) irrespective of the nature of the 4-substituent [26]. No spiro-products were detected even by GC–MS analyses of reaction mixtures. Byproducts included traces of imines ArC(R2)=NH (ImH

• was in good accordance with the observed exclusive formation of phenanthridines derived from radicals 5a–f for these compounds. The possibility of the rearrangement of spiro- to ortho-species via aziridinyl intermediates (or transition states) (az) which contain benzyl stabilization was examined

Synthesis of phenanthridines via palladium-catalyzed picolinamide-directed sequential C–H functionalization

• Ryan Pearson,
• Shuyu Zhang,
• Gang He,
• Nicola Edwards and
• Gong Chen

Beilstein J. Org. Chem. 2013, 9, 891–899, doi:10.3762/bjoc.9.102

• States of America 10.3762/bjoc.9.102 Abstract We report a new synthesis of phenanthridines based on palladium-catalyzed picolinamide-directed sequential C–H functionalization reactions starting from readily available benzylamine and aryl iodide precursors. Under the catalysis of Pd(OAc)2, the ortho-C–H

• ; palladium; phenanthridine; picolinamide; Introduction Phenanthridines and 5,6-dihydro-phenanthridines are important core structures found in a variety of natural products and functional molecules (Scheme 1A) [1][2][3][4][5][6][7][8]. Synthetic methods for their preparation include the classical Pictet

• strategies for synthesizing phenanthridines [23][24][25]. Despite these advances, construction of phenanthridines with complex substitution patterns remains difficult and often requires lengthy and inefficient synthetic sequences. Herein, we report a novel method for phenanthridine synthesis based on