DBU-Mediated Cyclization of Acylcyclopropanecarboxylates with Amidines: Access to Polysubstituted Pyrimidines

Synthesis of Fully Substituted Pyrazoles with a Dicyanomethyl Group via DBU/Lewis Acid-Mediated Annulation of D-A Cyclopropanes with Arylhydrazines

The efficient synthesis of fully substituted pyrazoles with a dicyanomethyl group was developed via an annulation reaction of 2-aroyl D-A cyclopropanes with arylhydrazines in the presence of DBU/AlCl3 reaction systems. This synthetic approach featured a wide range of readily available aroyl-substituted D-A cyclopropanes with diverse functional groups and a diversity of substituents on pyrazole products and had operationally simple and mild reaction conditions.

Annulation of 2-Aroyl D-A Cyclopropanes via Selectively Ring-Opening Process with o-Benzenediamines to Access Quinoxaline Derivatives

An annulation reaction of 2-aroyl D-A cyclopropanes with o-benzenediamines via selective cleavage of C-C bonds of cyclopropane in the presence of DBU/Sc(OTf)3 reaction systems was developed for the direct preparation of 2-aryl-3-benzylquinoxalines. This synthetic approach tolerated a wide range of readily available aroyl-substituted D-A cyclopropanes with diverse functional groups and had operationally simple and mild reaction conditions.

Six-Membered Aromatic Nitrogen Heterocyclic Anti-Tumor Agents: Synthesis and Applications

Cancer stands as a serious malady, posing substantial risks to human well-being and survival. This underscores the paramount necessity to explore and investigate novel antitumor medications. Nitrogen-containing compounds, especially those derived from natural sources, form a highly significant category of antitumor agents. Among these, antitumor agents with six-membered aromatic nitrogen heterocycles have consistently attracted the attention of chemists and pharmacologists. Accordingly, we present a comprehensive summary of synthetic strategies and clinical implications of these compounds in this review. This entails an in-depth analysis of synthesis pathways for pyridine, quinoline, pyrimidine, and quinazoline. Additionally, we explore the historical progression, targets, mechanisms of action, and clinical effectiveness of small molecule inhibitors possessing these structural features.

Acetic Acid-Catalyzed (3 + 2) Cyclization of 2-Aroyl-3-aryl-1,1-dicyanocyclopropanes with Arylhydrazines: To trans-4-Dicyanomethyl-1,3,5-triaryl-4,5-dihydropyrazoles

Acetic acid-catalyzed (3 + 2) cyclization reaction of substituted 2-aroyl-3-aryl-1,1-dicyanocyclopropanes with arylhydrazines was investigated for the efficient synthesis of 4-dicyanomethyl-1,3,5-triaryl-4,5-dihydropyrazoles in good yields, in which 4,5-double substituents are predominantly trans selective. This approach included the consecutive condensation, ring opening, and double nucleophilic cyclization reaction.

Acetic Acid Mediated Regioselective [3 + 3] Cycloaddition of Substituted Cyclopropane-1,1-dicarbonitriles with 1,4-Dithiane-2,5-diol

An acetic acid mediated regioselective [3 + 3] cycloaddition of substituted cyclopropane-1,1-dicarbonitriles with in situ generated mercaptoacetaldehyde was developed for the synthesis of highly stereoselective tetrahydrothiopyranols. This transformation created two new bonds in a single operation for generating complexity in tetrahydrothiopyrans. This method is characterized by cheap and readily available starting materials, simple operation, and mild reaction conditions.

Selective Synthesis of Substituted Pyridines and Pyrimidines through Cascade Annulation of Isopropene Derivatives

Diverse substituted pyridines and pyrimidines with high selectivity were obtained using a concise and efficient protocol developed herein. The reaction proceeds via metal-free cascade annulation of isopropene derivatives. Using isopropene derivatives as C3 synthons, NH₄I as the "N" source, and formaldehyde or dimethyl sulfoxide as the carbon source, this reaction realizes the efficient formation of intermolecular C-N and C-C bonds.

Yb(OTf)3-Mediated Annulation of Cyclopropane-1,1-dicarbonitriles with 2-Aminobenzaldehydes for Synthesis of Polysubstituted Quinolines

A Yb(OTf)₃-mediated annulation of cyclopropane-1,1-dicarbonitriles and 2-aminobenzaldehydes for the synthesis of polysubstituted quinolines in generally good yields was investigated. In the cascade reaction, the protocol includes ring opening, intermolecular nuclophilic addition, intramolecular nuclophilic addition, and demalononitrile aromatization, in which the malononitrile group serves as a deciduous directing group mediated by Yb(OTf)₃.

Iron-Catalyzed Alkyne-Based Multicomponent Synthesis of Pyrimidines under Air

An iron-catalyzed sustainable, economically affordable, and eco-friendly synthetic protocol for the construction of various trisubstituted pyrimidines is described. A wide range of trisubstituted pyrimidines were prepared using a well-defined, easy to prepare, bench-stable, and phosphine-free iron catalyst featuring a redox-noninnocent tridentate arylazo pincer under comparatively mild aerobic conditions via dehydrogenative functionalization of alcohols with alkynes and amidines.

Light-induced one-pot synthesis of pyrimidine derivatives from vinyl azides

A one-pot procedure for the synthesis of tetrasubstituted dihydropyrimidine and pyrimidine derivatives from α-azidocinnamates was developed. The synthesis is based on the finding that the outcome of LED photolysis of α-azidocinnamates depends on the light wavelength employed. Blue light (455 nm) leads to the formation of 2H-azirines only, but violet light (395 nm), UV-A light (365 nm), or sunlight result in the transformation of the in situ formed 2H-azirines to 1,3-diazabicyclo[3.1.0]hex-3-enes. Under basic catalysis (DBU), the latter were isomerized to 1,6-dihydropyrimidines which were oxidized to pyrimidines using DDQ. A successful use of Cs2CO3 as a base and air as an oxidant was also demonstrated.

Ring Opening of Donor-Acceptor Cyclopropanes with Acyclic 1,3-Diketones for the Synthesis of 1,6-Dicarbonyl Compounds

1,6-Dicarbonyl compounds, representing the formal addition products of the α-position of acetophenone derivatives to donor-acceptor cyclopropanes, were synthesized in two steps via first ring opening of donor-acceptor cyclopropanes with acyclic 1,3-diketones followed by DBU catalyzed retro-Claisen-type C-C bond cleavage reactions. In the first step, acyclic 1,3-diketones selectively worked as C-nucleophiles to add to donor-acceptor cyclopropanes. In the second step, the alkyl ketone part of the ring-opening products resulting from unsymmetrical 1,3-diketones was selectively cleaved in the presence of DBU in methanol.

DBU-promoted ring-opening reactions of multi-substituted donor–acceptor cyclopropanes: access to functionalized chalcones with a quaternary carbon group

A strategy to synthesize highly stereoselective chalcones with alkylcyanoacetate subunits via DBU-promoted ring-opening reactions of multi-substituted D–A cyclopropanes has been developed without the requirement of a transition metal catalyst and extra solvent.

Ring-opening reactions of donor–acceptor cyclopropanes with cyclic ketals and thiol ketals

Cyclic (thiol) ketals were used as hetero-nucleophiles for the ring opening of donor–acceptor cyclopropanes to afford functionalized diethers.