Combining Visible-Light-Photoredox and Lewis Acid Catalysis for the Synthesis of Indolizino[1,2-b]quinolin-9(11H)-ones and Irinotecan Precursor

The Intramolecular Povarov Tool in the Construction of Fused Nitrogen-Containing Heterocycles

Nitrogen heterocycles are part of the structure of natural products and agents with important biological activity, such as antiviral, antibiotic, and antitumor drugs. For this reason, heterocyclic compounds are one of today's most desirable synthetic targets and the Povarov reaction is a powerful synthetic tool for the construction of highly functionalized heterocyclic systems. This process involves an aromatic amine, a carbonyl compound, and an olefin or acetylene to give rise to the formation of a nitrogen-containing heterocycle. This review illustrates advances in the synthetic aspects of the intramolecular Povarov reaction for the construction of intricate nitrogen-containing polyheterocyclic compounds. This original review presents research done in this field, with references to important works by internationally relevant research groups on this current topic, covering the literature from 1992 to 2022. The intramolecular Povarov reactions are described here according to the key processes involved, using different combinations of aromatic or heteroaromatic amines, and aliphatic, aromatic, or heteroaromatic aldehydes. Some catalytic reactions promoted by transition metals are detailed, as well as the oxidative Povarov reaction and some asymmetric intramolecular Povarov processes.

Rapid Synthesis of Luotonin A Derivatives via Synergistic Visible-Light Photoredox and Acid Catalysis

The merging of visible-light photoredox and acid catalysis allowed for an intramolecular Povarov cycloaddition reaction using eosin Y as the photocatalyst and TsOH·H₂O as the co-catalyst. A visible-light-promoted dehydrogenative cyclization protocol enabled the construction of Luotonin A derivatives with up to 97% yield.

Visible-light-induced intramolecular radical cascade of α-bromo-N-benzyl-alkylamides: a new strategy to synthesize tetracyclic N-fused indolo[2,1-a]isoquinolin-6(5H)-ones

Polycyclic indole scaffolds are ubiquitous in pharmaceuticals and natural products and in materials science. Here, we present a visible-light-initiated intramolecular aryl migration/desulfonylation/cyclization cascade reaction for the synthesis of tetracyclic indolo[2,1-a]isoquinolin-6(5H)-ones. This protocol not only exhibited a wide substrate scope but also provided a mild route to access a variety of tetracyclic N-fused indoles.

[Cp*RhIII ]/Ionic Liquid as a Highly Efficient and Recyclable Catalytic Medium for C-H Amidation

A [Cp*Rh^III ]-catalyzed direct C-H amidation is carried out in ionic liquid. Both C(sp² )-H bonds of (hetero)arenes and alkenes and unactivated C(sp³ )-H bonds can be easily amidated with high functional-group tolerance and excellent yields under these conditions. Notably, using [Cp*Rh^III ]/[BMIM]BF₄ (BMIM=1-butyl-3-methylimidazolium) as the green and recyclable medium is environmentally benign, in light of characteristics such as the reusability of the expensive rhodium catalyst, avoidance of highly toxic organic solvents, and mild reaction conditions, as well as a short reaction time.

Recent advances of the Povarov reaction in medicinal chemistry

The Povarov multicomponent reaction consists on the condensation of an aniline, an aldehyde, and an activated olefin to generate a tetrahydroquinoline adduct with 3 diversity points. Hereby, we report the main features of this transformation and its uses in medicinal chemistry. Relevant examples of the impact of Povarov adducts in different therapeutic areas are provided.

Substituted 1,5-naphthyridine derivatives as novel antileishmanial agents. Synthesis and biological evaluation

Visceral leishmaniasis is a parasitic disease that affects, among other areas, both sides of the Mediterranean Basin. The drugs classically used in clinical practice are pentavalent antimonials (Sb^V) and amphotericin B, which are nephrotoxic, require parenteral administration, and increasing drug resistance in visceral leishmaniasis has been observed. These circumstances justify the search of new families of compounds to find effective drugs against the disease. Eukaryotic type I DNA topoisomerase (TopIB) has been found essential for the viability of the parasites, and therefore represents a promising target in the development of an antileishmanial therapy. In this search, heterocyclic compounds, such as 1,5-naphthyridines, have been prepared by cycloaddition reaction between N-(3-pyridyl)aldimines and acetylenes and their antileishmanial activity on promastigotes and amastigote-infected splenocytes of Leishmania infantum has been evaluated. In addition, the cytotoxic effects of newly synthesized compounds were assessed on host murine splenocytes in order to calculate the corresponding selective indexes (SI). Excellent antileishmanial activity of 1,5-naphthyridine 19, 21, 22, 24 and 27 has been observed with similar activity than the standard drug amphotericin B and higher selective index (SI > 100) towards L. infantum amastigotes than amphotericin B (SI > 62.5). Special interest shows the 1,5-naphthyridine 22 with an IC₅₀ value (0.58 ± 0.03 μM) similar to the standard drug amphotericin B (0.32 ± 0.05 μM) and with the highest selective index (SI = 271.5). In addition, this compound shows remarkable inhibition on leishmanial TopIB. However, despite these interesting results, further studies are needed to disclose other potential targets involved in the antileishmanial effect of these novel compounds.