Redox Condensations of o-Nitrobenzaldehydes with Amines under Mild Conditions: Total Synthesis of the Vasicinone Family

Photochemical cascade cyclization of quinazolinone-tethered unactivated alkenes with α-halocarbonyls toward 2,3-fused quinazolinones

The divergent synthesis of 2,3-fused quinazolinones via photocatalytic tandem cyclization has been disclosed. It features green reaction conditions, good functional group compatibility and applicability to gram-scale synthesis. In particular, the precursors of tertiary carbon radicals with high steric hindrance are suitable for this reaction. Mechanistic experiments indicate that a radical cascade cross-coupling/cyclization process is involved. This is an efficient example demonstrating the direct activation of inactive α-halocarbonyls to furnish alkyl radicals for the synthesis of polycyclic quinazolinones.

Alkaloids from Mackinlaya species and synthetic mackinazolinone derivatives: An overview

Mackinazolinone is the main alkaloid isolated from plants of the genus Mackinlaya, essentially distributed in tropical Asia and Australia. There are five Mackinlaya species all containing bioactive alkaloids with a tetrahydropyridoquinazolinone core such as mackinazoline (1) and mackinazolinone (2). The present review retraces the origin of mackinazolinone and compares the different chemical routes to synthesize the natural product, through different methods including classical batch synthesis, solid-phase supported synthesis, microwaved irradiation and photochemistry. A panel of about 70 mackinazolinone analogues and derivatives is presented to illustrate the diversity of chemical approaches and structures. The pharmacology of mackinazolinone has been little investigated but derivatives with antibacterial or anticancer properties have been identified. The molecular targets for these compounds are essentially unknown, but a few proteins of interest have been evoked occasionally, such as the EGFR kinase. The natural product mackinazolinone has largely inspired chemists to develop novel products and chemical processes. Hopefully, the review will now encourage pharmacologists to further explore the properties of these quinazolinones as potential anti-infectious, anticancer and/or neuroprotective agents.

Medium-Ring Keto Bislactams with Antischistosomal Activity

We discovered medium-ring keto bislactams as a new antischistosomal chemotype. The ketone functional group and isoindolinone substructure were required for high antischistosomal activity. Aryl substitution with EWG functional groups decreased the chemical stability. These compounds were relatively polar with the measured LogD7.4 values ranging from <0 to 2.4, had kinetic aqueous solubilities between 40 and >320 μM, and had relatively low cytotoxicities with IC50s ranging from 52 to >390 μM. We identified two compounds with IC50 values < 5 μM against ex vivoSchistosoma mansoni (S. mansoni).

Photoredox/HAT-Catalyzed Intramolecular Hydrocyclization of Alkenes toward 2,3-Fused Quinazolinones and Dihydroquinazolinones

New photochemical approaches to 2,3-fused quinazolinones and dihydroquinazolinones are disclosed. The intramolecular hydrocyclization proceeds in moderate to excellent yields across diverse alkenes with high regioselectivity and diastereocontrol. Mechanistic studies indicated that the radical cascade processes involve thiophenol acting as single-electron transfer and hydrogen atom transfer reagents. The success of the gram-scale synthesis proves the strategy can be used for practical applications.

One-Pot Stereoselective Synthesis of the Naphthofurano-Iminosugars via a [3 + 2] Cycloaddition Reaction

This study presents the synthesis of novel naphthofurano-iminosugars (4) using 2,3-O-isopropylidene D-ribose tosylate (1a), anilines (2), and 1,4-benzoquinone (3a) as starting materials through key iminium ion/enamine intermediates via [3 + 2] cyclization reactions at room temperature. The reaction has unique regioselectivity and stereoselectivity with moderate to excellent yields. The adaptability of this method has been demonstrated using various substituted anilines, on which both electron-donating and electron-withdrawing groups were well employed in the reactions. Notably, the treatment of the fused multicyclic iminosugar 4 with TFA efficiently leads to an interesting unexpected pyridinium salt (8), possible via four sequential steps: deprotection of the 2,3-O-isopropylidene group, furan ring opening, dehydration condensation of the OH groups, and elimination of water.

Recent Advances in the Research on Luotonins A, B, and E

This digest review summarises the most recent progress in the study on luotonins A, B and E. The literature covered in this overview spans from January 2012 to April 2024 and presents synthetic methodologies for the assembly of the quinolinopyrrolo-quinazoline scaffold, the structural motifs present in luotonins A, B, and E, and the evaluation of the biological activities of their derivatives and structural analogues.

Access to N-Fused Quinazolinones by Radical-Promoted Cascade Annulations of Alkenyl N-Cyanamides with Aromatic Aldehydes

A cascade radical cyclization of alkenyl N-cyanamides with aromatic aldehydes has been achieved for an expeditious synthesis of keto-methylated dihydropyrrolo-quinazolinones. Benzoyl radicals, generated from aryl aldehydes in the presence of di-tert-butyl peroxide (DTBP), promoted the domino annulations leading to distinctive functionalized quinazolinones in good yields. In addition, the robustness of the present protocol is validated by employing heterocyclic and natural product-based aldehydes.

Discovery of extended product structural space of the fungal dioxygenase AsqJ

The fungal dioxygenase AsqJ catalyses the conversion of benzo[1,4]diazepine-2,5-diones into quinolone antibiotics. A second, alternative reaction pathway leads to a different biomedically important product class, the quinazolinones. Within this work, we explore the catalytic promiscuity of AsqJ by screening its activity across a broad range of functionalized substrates made accessible by solid-/liquid-phase peptide synthetic routes. These systematic investigations map the substrate tolerance of AsqJ within its two established pathways, revealing significant promiscuity, especially in the quinolone pathway. Most importantly, two further reactivities leading to new AsqJ product classes are discovered, thus significantly expanding the structural space accessible by this biosynthetic enzyme. Switching AsqJ product selectivity is achieved by subtle structural changes on the substrate, revealing a remarkable substrate-controlled product selectivity in enzyme catalysis. Our work paves the way for the biocatalytic synthesis of diverse biomedically important heterocyclic structural frameworks.

Metal-Catalyzed Cascade Reactions between Alkynoic Acids and Dinucleophiles: A Review

Cascade reactions provide a straightforward access to many valuable compounds and reduce considerably the number of steps of a synthetic sequence. Among the domino and multicomponent processes that involve alkynes, the cascade reaction between alkynoic acids and C-, N-, O- and S-aminonucleophiles stands out as a particularly powerful tool for the one-pot construction of libraries of nitrogen-containing heterocyclic compounds with scaffold diversity and molecular complexity. This reaction, based on an initial metal-catalyzed cycloisomerization that generates an alkylidene lactone intermediate, was originally catalyzed by gold(I) catalysts, along with silver salts or Brönsted acid additives, but other alternative metal catalysts have emerged in the last decade as well as different reaction media. This review examines the existing literature on the topic of metal-catalyzed cascade reactions of acetylenic acids and dinucleophiles and discusses aspects concerning substrate/catalyst ratio for every catalyst system, nature of the aminonucleophile involved and substrate scope. In addition, alternative solvents are also considered, and an insight into the pathway of the reaction and possible intermediates is also provided.

Sodium Hypophosphite as a Bulk and Environmentally Friendly Reducing Agent in the Reductive Amination

NaH₂PO₂ was found to promote reductive amination. Being nontoxic, stable, environmentally benign, and available in bulk amounts, this reducing agent showed a powerful potential to compete with classical reductants applied in the target process. An E factor of 1 was achieved for the substrate scope. Different carbonyl compounds reacted with amines under the developed conditions. The reaction demonstrated a great compatibility with a wide range of functional groups. Reaction conditions were scaled up to 200-fold.

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.

Condensation-Based Methods for the C-H Bond Functionalization of Amines

This review aims to provide a comprehensive overview of condensation-based methods for the C-H bond functionalization of amines that feature azomethine ylides as key intermediates. These transformations are typically redox-neutral and share common attributes with classic name reactions such as the Strecker, Mannich, Friedel-Crafts, Pictet-Spengler, and Kabachnik-Fields reaction, while incorporating a redox-isomerization step. This approach provides an ideal platform to rapidly transform simple starting materials into complex amines.

Enantioselective Copper-Catalyzed Borylative Cyclization for the Synthesis of Quinazolinones

Quinazolinones are common substructures in molecules of medicinal importance. We report an enantioselective copper-catalyzed borylative cyclization for the assembly of privileged pyrroloquinazolinone motifs. The reaction proceeds with high enantio- and diastereocontrol, and can deliver products containing quaternary stereocenters. The utility of the products is demonstrated through further manipulations.

Chemoselective Reactions of Isocyanates with Secondary Amides: One-Pot Construction of 2,3-Dialkyl-Substituted Quinazolinones

A facile method for the preparation of 2,3-dialkyl-substituted quinazolinones from readily available N-arylamides and commercial isocyanates was developed. This one-pot procedure involves the chemoselective activation of the secondary amide with Tf₂O/2-Br-Pyr, the sequential addition of isocyanate, and cyclization. The mild reaction is general for a wide range of substrates and can be run on a gram scale.

Self-Catalyzed Phototandem Perfluoroalkylation/Cyclization of Unactivated Alkenes: Synthesis of Perfluoroalkyl-Substituted Quinazolinones

A novel visible-light-induced radical tandem trifluoromethylation/cyclization of unactivated alkenes with sodium perfluoroalkanesulfinates (R_f = CF₃, C₃F₇, C₄F₉, C₆F₁₃, C₈F₁₇) under air atmosphere has been developed. A range of quinazolinones containing unactivated alkene moiety and sodium perfluoroalkanesulfinates were compatible with this transformation, leading to a variety of perfluoroalkyl-substituted quinazoline alkaloids. Remarkably, the experiment can be carried out without any metal catalyst, strong oxidant, or external photosensitizer.

Sc(OTf)3-catalyzed [3 + 2]-cycloaddition of nitrones with ynones

An efficient approach to access functionalized (2,3-dihydroisoxazol-4-yl) ketones has been developed by reacting nitrones 4 with ynones 7 or terminal ynones 10 in a one-pot fashion. The reaction went through a formal Sc(OTf)3-catalyzed [3 + 2]-cycloaddition process to generate a number of functionalized (2,3-dihydroisoxazol-4-yl) ketones 11aa-11aw, 11ba-11la and 12aa-12ae in moderate to good yields.