Synthesis of 6-Trichloromethylphenanthridines by Transition Metal-Free Radical Cyclization of 2-Isocyanobiphenyls

Redox-Neutral Cyclization of 2-Isocyanobiaryls through Photoredox/PPh3 Dual Catalysis

The photoredox/PPh3-mediated cyclization of 2-isocyanobiaryls has been developed. A substantial range of functional-group-rich phenanthridine derivatives were synthesized at room temperature in a highly selective and atom-economic manner. Mechanistic studies suggested that the cyclization process is probably mediated both by Ph3P radical cation with key 1,2-hydride transfer and hydrogen atom generated through O-H bond homolytic cleavage of Ph3P-OH radical intermediate.

Visible Light-Promoted Radical-Mediated Ring-Opening/Cyclization of Vinyl Benzotriazoles: An Alternative Approach to Phenanthridines

A visible light-promoted radical-mediated ring-opening/cyclization of vinyl benzotriazoles has been developed. The method provides an efficient and practical approach to synthesize functionalized phenanthridines from vinyl benzotriazoles with alkyl bromides under mild conditions. Significantly, the readily available and bench-stable vinyl benzotriazoles can serve as valuable alternative radical acceptors during the synthesis of phenanthridines.

Copper(i)-catalyzed radical carboamination reaction of 8-aminoquinoline-oriented buteneamides with chloroform: synthesis of-β-lactams

A novel Cu(CH₃CN)₄PF₆-catalyzed carboamination reaction of 8-aminoquinoline-oriented buteneamides with chloroform to afford 4-(2,2,2-trichloroethyl)-β-lactams is described. The reaction proceeded at 110 °C in air with di-t-butyl peroxide. Preliminary studies indicated that the reaction undergoes a free radical mechanism via a Cu(i)/Cu(ii)/Cu(iii) catalytic cycle.

Oxidative Photocyclization of Aromatic Schiff Bases in Synthesis of Phenanthridines and Other Aza-PAHs

The oxidative photocyclization of aromatic Schiff bases was investigated as a potential method for synthesis of phenanthridine derivatives, biologically active compounds with medical applications. Although it is possible to prepare the desired phenanthridines using such an approach, the reaction has to be performed in the presence of acid and TEMPO to increase reaction rate and yield. The reaction kinetics was studied on a series of substituted imines covering the range from electron-withdrawing to electron-donating substituents. It was found that imines with electron-withdrawing substituents react one order of magnitude faster than imines bearing electron-donating groups. The ¹H NMR monitoring of the reaction course showed that a significant part of the Z isomer in the reaction is transformed into E isomer which is more prone to photocyclization. The portion of the Z isomer transformed showed a linear correlation to the Hammett substituent constants. The reaction scope was expanded towards synthesis of larger aromatic systems, namely to the synthesis of strained aromatic systems, e.g., helicenes. In this respect, it was found that the scope of oxidative photocyclization of aromatic imines is limited to the formation of no more than five ortho-fused aromatic rings.

Synthesis and Anticancer Activity Evaluation of Novel Phenanthridine Derivatives

Based on the structure of sanguinarine, fourteen phenanthridine derivatives were designed and synthesized in the current study. The cytotoxic activities of synthesized compounds were evaluated against five human cancer cell lines (MCF-7, PC3, Hela, A549, and HepG2 cell lines) via MTT assay. Among all the compounds tested, molecule 8a exhibited significant cytotoxic activity against MCF-7 cells with a IC₅₀ value of 0.28 μM. A following up enzymatic assay indicated that compound 8a could inhibit the activity of DNA topoisomerase I/II. Further mechanistic studies performed in the MCF-7 cell line revealed that compound 8a could arrest cell cycle in S phase and induce cell apoptosis via downregulation of Bcl-2 and upregulation of Bax. Collectively, a potent DNA topoisomerase inhibitor (8a) was discovered, which exhibited potential as a candidate chemotherapeutic agent for the management of tumors in the present study.

Convenient synthesis of 6-alkyl phenanthridines and 1-alkyl isoquinolines via silver-catalyzed oxidative radical decarboxylation

A convenient and efficient protocol for the synthesis of 6-alkyl phenanthridines and 1-alkyl isoquinolines has been developed. The reaction relies on the coupling of 2-isocyanobiphenyls and vinyl isonitriles with alkyl radicals formed by the silver-catalyzed decarboxylation of stoichiometric aliphatic carboxylic acids, and affords diverse phenanthridine and isoquinoline derivatives under mild reaction conditions. The experiment of β-scission of cyclobutylcarbinyl radicals is used to shed light on the reaction mechanism.

Cobalt-catalyzed radical cyclization of isocyanides forming phenanthridine derivatives

A neutral cobalt(ii) compound catalyzes the radical cyclization of 2-isocyano-biphenyls with various alkyl halides, providing a series of phenanthridine-fused polycycles.

Iron-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes: a highly efficient approach to 6-benzylated phenanthridines

A highly efficient Fe-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes for the synthesis of 6-benzylated phenanthridines has been reported.

Transition-metal-free synthesis of 3-(1-pyrrolidinyl)quinolines and 3-(1-pyrrolidinyl)quinoline 1-oxides via a one-pot reaction of 3-(1-pyrrolidinyl)crotonates with nitrobenzenes

A carbanion of tert-butyl 3-(1-pyrrolidinyl)crotonate adds to nitrobenzenes to form σ^H-adducts, which in the presence of pivaloyl chloride and triethylamine are converted into 3-(1-pyrrolidinyl)quinolines or 3-(1-pyrrolidinyl)quinoline 1-oxides depending on the nitrobenzene structure. This is the first methodology in which a quinoline ring is constructed from a substrate bearing a pyrrolidinyl ring. Starting from optically pure enamines, the method allows synthesis of the corresponding chiral products without racemisation.

Active methylene compounds (AMCs) controlled facile synthesis of acridine and phenanthridine from morita Baylis–Hillman acetate

We carried out simple and facile syntheses of acridines and phenanthridines from MBH acetates of 2-chloro-quinoline-3-carbaldehyde with active methylene compounds (AMCs).

Visible-light-mediated radical insertion/cyclization cascade reaction: synthesis of phenanthridines and isoquinolines from isocyanides

The development of a visible-light promoted radical insertion/cyclization cascade reaction to generate phenanthridines and isoquinolines from isocyanides under mild reaction conditions is reported.