A copper(II)-catalyzed, sequential Michael–aldol reaction for the preparation of 1,2-dihydroquinolines

Mechanistic Insights from Density Functional Theory into Rh/Acid-Catalyzed Synthesis of 1,2-Dihydroquinolines via Skeleton-Reorganizing Coupling of Cycloheptatriene and Amines

Density functional theory calculations were conducted to refine our understanding at the molecular level of the synthesis of fused 1,2-dihydroquinolines through Rh- and acid-catalyzed skeleton-reorganizing coupling reactions of cycloheptatriene with amines. The results reveal that the reaction progresses via cascade catalysis, consisting of consecutive steps of Rh-catalyzed intermolecular coupling involving two RhIII-RhI-RhIII transformations with a maximum energy barrier of 27.1 kcal/mol, followed by acid-catalyzed intramolecular skeleton reorganization with a peak energy barrier of 23.3 kcal/mol. The most significant finding of this work is the identification of a new oxidation-reduction mode of the Rh center. This mode is achieved via migration of a proton from the ammonium ion to the metal center and nucleophilic attack-induced intermolecular reductive coupling, distinguishing it from the conventional oxidative addition-reductive elimination process. The acid-catalyzed intramolecular skeleton reorganization necessitates the assistance of a second HOTs molecule, along with its conjugate base, which sequentially facilitates retro-Mannich-type C-C cleavage and the isomerization of the terminal imine to enamine via acid-base catalysis. Our calculations also explain why the azabicyclic tropene byproduct does not compete with the formation of the fused 1,2-dihydroquinoline product. These theoretical insights are expected to provide valuable guidance for further improvements in the efficiency of skeleton-reorganizing coupling reactions between cycloheptatriene and amines.

Synthesis of Functionalized Tetrahydroquinoline Containing Indole Scaffold via Chemoselective Annulation of Aza-ortho-quinone Methide Precursor

The chemoselective annulation of aza-ortho-quinone methide generated by in situ o-chloromethyl sulfonamide has been achieved with bifunctional acyclic olefin. This efficient approach provides access to the diastereoselective synthesis of functionalized tetrahydroquinoline derivatives containing indole scaffolds through the inverse-electron-demand aza-Diels-Alder reaction under mild reaction conditions with excellent results (up to 93% yield, > 20:1 dr). Moreover, this article realized the cyclization of α-halogeno hydrazone with electron-deficient alkene affording the tetrahydropyridazine derivatives, which had never been reported.

Chemodivergent Synthesis of Aza-Heterocycles with a Quarternary Carbon Center via [4 + 1] Annulation between Azoalkenes and α-Bromo Carbonyl Compounds

An efficient [4 + 1] annulation reaction between in situ generated azoalkene intermediates and α-bromocarbonyls has been established. A series of skeletally diverse aza-heterocycles with a functionalized quaternary center were obtained in up to 89% yield under mild conditions.

Solvent-Free Mechanosynthesis of Polysubstituted 1,2-Dihydroquinolines from Anilines and Alkyne Esters

A novel one-pot reaction of anilines with acetylenedicarboxylate diesters in the presence of boron trifluoride, iodine, and trifluoroacetic acid or methylsulfonic acid has been developed under solvent-free ball-milling conditions, affording a variety of polysubstituted 1,2-dihydroquinolines bearing multiple ester groups in moderate to excellent yields. The present protocol features mild reaction conditions, short reaction time, and feasibility of large-scale synthesis, providing a facile and practical alternative to 1,2-dihydroquinoline synthesis. Intriguingly, the generated 1,2-dihydroquinolines can be further transformed into quinoline derivatives.

Synthesis of polysubstituted 1,2-dihydroquinolines and indoles via cascade reactions of arylamines and propargylic alcohols catalyzed by FeCl3·6H2O

Syntheses of 1,2-dihydroquinolines from arylamines and propargylic alcohols via cascade Friedel–Crafts-type reaction and 6-endo-trig hydroamination catalyzed by FeCl₃·6H₂O are described.

Efficient synthesis of functionalized dihydroquinolines, quinolines and dihydrobenzo[b]azepine via an iron(iii) chloride-catalyzed intramolecular alkyne–carbonyl metathesis of alkyne tethered 2-amino benzaldehyde/acetophenone derivatives

Iron-catalyzed synthesis of dihydroquinolines, quinolines and dihydrobenzo[b]azepine.

Enantioselective approach to quinolizidines: total synthesis of cermizine D and formal syntheses of senepodine G and cermizine C

The formal syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselective, intramolecular amide Michael addition process. The total synthesis of cermizine D has been achieved through use of an organocatalyzed, heteroatom Michael addition to access a common intermediate. Additional key steps of this sequence include a matched, diastereoselective alkylation with an iodomethylphenyl sulfide and sulfone-aldehyde coupling/reductive desulfurization sequence to combine the major subunits. The utility of a Hartwig-style C-N coupling has been explored on functionally dense coupling partners. Diastereoselective conjugate additions to α,β-unsaturated sulfones have been investigated, which provided the key sulfone intermediate in just six steps from commercially available starting materials. The formal syntheses of senepodine G and cermizine C have been accomplished through an intramolecular cyclization process of a N-Boc-protected piperidine sulfone.