Visible-Light-Mediated Annulation/Thiolation of 2-Isocyanobiaryls with Disulfides to Organoylthiophenanthridines Derivatives

A visible-light-induced annulation/thiolation of 2-isocyanobiaryls with dialkyl(aryl)disulfides has been established, delivering a sustainable and atom-economic route to 6-organoylthiophenanthridines with wild functional group tolerance and good to excellent yields under oxidant-, base-, and transition-metal-free conditions.

Selective access to dihydrophenanthridines and phenanthridinones via cyclisation of aryl amines onto N-tethered arynes

5,6-Dihydrophenanthridines are prepared from aryl amines via intramolecular addition to N-tethered arynes under mild conditions. A new o-silylaryl triflate precursor was developed to increase reactivity and enable electron-rich and electron-poor aryl amines to undergo cyclisation. A complete switch in product selectivity occurs when the reaction is conducted in air, affording the corresponding phenanthridin-6(5H)-one as the sole product under otherwise identical reaction conditions.

NHC-alcohol adduct-mediated photocatalytic deoxygenation for the synthesis of 6-phenanthridine derivatives

NHC-alcohol adduct-mediated deoxygenation of alcohols under photocatalytic conditions is described. This process provides various alkyl radicals, which can react with 2-isocyanobiaryls to afford 6-substituted phenanthridine derivatives in moderate to good yields. This method offered the first example of directly using alcohols as radical sources for 6-phenanthridine synthesis.

Bischler-Napieralski Synthesis of 6-Alkynyl Phenanthridines Based on Tf2O-Promoted Electrophilic Activation of N-Aryl-2-propynamides

An efficient method for the synthesis of 6-alkynyl phenanthridines was developed. The method offered the first example to use 2-propynamides as substrates in the Bischler-Napieralski reaction and to create alkynylnitrilium triflates as new active intermediates in organic synthesis.

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

TfOH-promoted Classical Nazarov-type Cyclization of Benzofulvenes: Synthesis of Polycyclic 5H,10'H-spiro[benzo[k]phenanthridine-5,6'-dibenzopentalenes]

The reaction of o-benzofulvene with TfOH leads to intramolecular cyclization through novel C-C and C-N bond formation, resulting in the formation of 5H,10'H-spiro[benzo[k]phenanthridine-5,6'-dibenzopentalene]. This protocol provides a new molecular framework with reasonable to excellent yields and tolerates various electron-withdrawing/donating substituents. This method yields diastereoselectivity of up to >20:1. Furthermore, it is free of bases, oxidants, and metals and proceeds under mild reaction conditions, which are favorable for synthetic organic chemistry.

Recent Advances on Photoinduced Cascade Strategies for the Synthesis of N-Heterocycles

Over the last decade, visible-light photocatalysis has proved to be a powerful tool for the construction of N-heterocyclic frameworks, important constituents of natural products, insecticides, pharmacologically relevant therapeutic agents and catalysts. This account highlights recent developments and established methods towards the photocatalytic cascades for preparation of different classes of N-heterocycles, giving emphasis on our contribution to the field.

Discovery of 7-aminophenanthridin-6-one as a new scaffold for matrix metalloproteinase inhibitors with multitarget neuroprotective activity

Matrix metalloproteinases (MMPs) are zinc-dependent hydrolytic enzymes of great biological relevance, and some of them are key to the neuroinflammatory events and the brain damage associated to stroke. Non-zinc binding ligands are an emerging trend in drug discovery programs in this area due to their lower tendency to show off-target effects. 7-Amino-phenanthridin-6-one is disclosed as a new framework able to inhibit matrix metalloproteinases by binding to the distal part of the enzyme S1' site, as shown by computational studies. A kinetic study revealed inhibition to be noncompetitive. Some of the compounds showed some degree of selectivity for the MMP-2 and MMP-9 enzymes, which are crucial for brain damage associated to ischemic stroke. Furthermore, some compounds also had a high neuroprotective activity against oxidative stress, which is also very relevant aspect of ischaemic stroke pathogenesis, both decreasing lipid peroxidation and protecting against the oxidative stress-induced reduction in cell viability. One of the compounds, bearing a 2-thienyl substituent at C-9 and a 4-methoxyphenylamino at C-7, had the best-balanced multitarget profile and was selected as a lead on which to base future structural manipulation.

Vanadium(V) Complex-Catalyzed One-Pot Synthesis of Phenanthridines via a Pictet-Spengler-Dehydrogenative Aromatization Sequence

Phenanthridine and its derivatives are important structural motifs that exist in natural products, biologically active compounds, and functional materials. Here, we report a mild, one-pot synthesis of 6-arylphenanthridine derivatives by a sequential cascade Pictet-Spengler-dehydrogenative aromatization reaction mediated by oxovanadium(V) complexes under aerobic conditions. The reaction of 2-(3,5-dimethoxyphenyl)aniline with a range of commercially available aryl aldehydes provided the desired phenanthridine derivatives in up to 96% yield. The ability of vanadium(V) complexes to function as efficient redox and Lewis acid catalysts enables the sequential reaction to occur under mild conditions.

Energy transfer-driven regioselective synthesis of functionalized phenanthridines by visible-light Ir photocatalysis

A photocatalytic strategy for selective synthesis of 2-substituted phenanthridines from N-iminylpyridinium salts has been developed.

Fluoroalkylation of Various Nucleophiles with Fluoroalkyl Sulfones through a Single Electron Transfer Process

The fluoroalkylation of various nucleophilic reagents with (phenylsulfonyl)difluoromethyl (PhSO₂CF₂)-substituted phenanthridines was achieved to give fluorinated phenanthridine derivatives, which enables the construction of both carbon-heteroatom and carbon-carbon bonds via the substitution of the phenylsulfonyl group. Mechanistic studies indicated that these reactions proceed through a unimolecular radical nucleophilic substitution (S_RN1) mechanism. It is worthwhile noting that in the cases of O-nucleophiles ( t-BuO^- and PhO^-), the addition of t-BuOK/PhCHO could significantly promote the reactions, due to the in situ formation of a highly reactive electron donor species through the interaction of t-BuOK, PhCHO, and the solvent DMF, which can effectively initiate the single electron transfer process.

Palladium-catalyzed decarbonylative annulation of phthalimides with arynes: direct construction of phenanthridinones

A novel palladium-catalyzed decarbonylative annulation between phthalimides and arynes was well-established, affording phenanthridinone derivatives in moderate to good yields.

Nickel-Catalyzed Oxidative Decarboxylative Annulation for the Synthesis of Heterocycle-Containing Phenanthridinones

A nickel-catalyzed oxidative decarboxylative annulation reaction of simple benzamides and (hetero)aromatic carboxylates has been developed. This reaction provides access to a large array of phenanthridinones and their heterocyclic analogues, highlighting the utility and versatility of oxidative decarboxylative coupling strategies for C-C bond formation.

A Review on Recent Syntheses of Amaryllidaceae Alkaloids and Isocarbostyrils (Time period mid-2016 to 2017)

Alkaloids from the Amaryllidaceae have become valuable targets for synthetic organic chemists, mainly due to their wide variety of bioactivities and potential for utilization in medicinal chemistry ventures. In addition, the structural complexity of a number of these alkaloids has also been a reason for the interest in these compounds. In this review, the last 18 months of literature was perused and synthetic highlights have been presented here, with the hope to further focus attention on this interesting class of compounds and to encourage others to synthesize these compounds and their derivatives and/or analogues. The review contains examples of syntheses from most of the important alkaloid scaffold classes previously isolated from the Amaryllidaceae, namely: lycorine, crinine, galanthamine, tazettine, montanine, phenanthridone, phenanthridine, plicamine, mesembrine and some minor scaffolds (like gracilamine).

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.