Synthesis of 2-Indolyltetrahydroquinolines by Zinc(II)-Catalyzed Intramolecular Hydroarylation-Redox Cross-Dehydrogenative Coupling of N -Propargylanilines with Indoles

Direct Regioselective Hydro(hetero)arylation/Cyclocondensation Reactions of β-(2-Aminophenyl)-α,β-ynones by Means of Transition-Metal Catalysis/Brønsted Acid Synergism: Experimental Results and Computational Insights

Experimental results and computational insights explain the key role of transition-metal catalysis/Brønsted acid synergism in the achievement of the sequential regioselective direct heteroarylation/cyclocondensation reactions of β-(2-aminophenyl)-α,β-ynones with a variety of electron-rich aromatic heterocyclic/arenes to afford quinoline-(hetero)aromatic hybrids. The first approach to the synthesis of 4-(1H-pyrrol-2-yl)quinolines is described. The effectiveness of various transition metals is compared.

Copper(I)-catalysed intramolecular hydroarylation-redox cross-dehydrogenative coupling of N-propargylanilines with phosphites

Intramolecular hydroarylation-redox cross-dehydrogenative coupling of N-propargylanilines with phosphite diesters proceeded in the presence of Cu(I)-catalysts (20 mol%) to selectively give 2-phosphono-1,2,3,4-tetrahydroquinolines in good yields with 100% atomic utilization. P-H and two C-H bonds are activated at once and these hydrogen atoms are trapped by a propargylic triple bond in the molecule.

Stereoselective Synthesis of Hexahydroimidazo[1,2-a]quinolines via SN2-Type Ring-Opening Hydroarylation-Hydroamination Cascade Cyclization of Activated Aziridines with N-Propargylanilines

A novel synthetic approach for the construction of 1,2,3,3a,4,5-hexahydroimidazo[1,2-a]quinolines in good yields (up to 75%) with excellent stereoselectivity (dr up to 94:6, ee up to >99%) under one-pot domino ring-opening cyclization (DROC) conditions has been developed. The DROC protocol proceeds through a Lewis acid catalyzed S_N2-type ring-opening of activated aziridines with N-propargylanilines followed by intramolecular cyclization comprising concomitant hydroarylation and hydroamination steps in a domino fashion.

Zinc(ii)-catalyzed intramolecular hydroarylation-redox cross-dehydrogenative coupling of N-propargylanilines with diverse carbon pronucleophiles: facile access to functionalized tetrahydroquinolines

Zinc(ii)-catalyzed intramolecular hydroarylation-redox cross-dehydrogenative coupling of N-propargylanilines with two types of carbon pronucleophiles (nitromethane as a sp³ carbon pronucleophile and phenylacetylenes as sp carbon pronucleophiles) proceeded to give the 2-substituted tetrahydroquinolines in good yields with 100% atomic utilization without any additional external oxidants.

Catalytic C3 aza-alkylation of indoles

The aza-alkylation reaction at position 3 of the indole scaffold allows the introduction of a differently substituted aminomethyl group, with the formation of a stereogenic centre. Critical summary of 2000–2019 meaningful papers.

Zn(OTf)2-mediated annulations of N-propargylated tetrahydrocarbolines: divergent synthesis of four distinct alkaloidal scaffolds

Experimental and computational studies gained insights into Zn(OTf)₂-mediated annulations and allowed programmable synthesis of four distinct alkaloidal scaffolds.

Intramolecular hydroarylations of N-propargylated tetrahydrocarbolines were efficiently mediated using a unique combination of Zn(OTf)₂ with t-BuOH under neutral conditions. Use of the artificial force induced reaction method in the global reaction route mapping strategy provided insights into the Zn(OTf)₂-mediated hydroarylations and the associated intriguing solvent effects of t-BuOH facilitating a protodezincation process without a Brønsted acid activator. We systematically implemented three distinct hydroarylations as well as an unanticipated α-alkenylation of a carbonyl group to obtain the four alkaloidal scaffolds 2–4, and 18. Zn(OTf)₂-mediated annulation of 1c proceeded through kinetic formation of the spiroindole 3c followed by an alkenyl shift and concomitant retro-Mannich-type fragmentation to furnish azepino[4,5-b]indole 2 framework. Substituents on substrate 1 in the vicinity of the reaction sites substantially affected the mode of the divergent annulations. Judicious choices of the substituents, solvent and reaction conditions enabled programmable divergent synthesis of the four distinct skeletons.

Palladium-Catalyzed Regioselective Syn-Chloropalladation-Olefin Insertion-Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Oxidative Asymmetric Formal Aza-Diels⁻Alder Reactions of Tetrahydro-β-carboline with Enones in the Synthesis of Indoloquinolizidine-2-ones

Ru-catalyzed tandem amine oxidative dehydrogenation/formal aza-Diels⁻Alder reaction for enantio- and diastereoselective synthesis of indoloquinolizidine-2-ones from tetrahydro-β-carbolines and α,β-unsaturated ketones is described. The reaction proceeds via tandem ruthenium-catalyzed amine dehydrogenation using tert-butyl hydroperoxide (TBHP) as the oxidant and a chiral thiourea-catalyzed formal aza-[4 + 2] cycloaddition, providing a step-economical strategy for the synthesis of these valuable heterocyclic products.

3-Dialkylamino-1,2,4-triazoles via ZnII-Catalyzed Acyl Hydrazide-Dialkylcyanamide Coupling

Zinc(II)-catalyzed (10 mol % ZnCl₂) coupling of acyl hydrazides and dialkylcyanamides in ethanol leads to 3-dialkylamino-1,2,4-triazoles (76-99%; 17 examples). This reaction represents a novel, straightforward, and high-yielding approach to practically important 3-NR₂-1,2,4-triazoles, which utilizes commercially available and/or easily generated substrates. Seventeen new 3-NR₂-1,2,4-triazoles were characterized by HRESI⁺-MS and IR, ¹H, and ¹³C{¹H} NMR spectroscopies and five species additionally by single-crystal X-ray diffraction (XRD). The Zn^II-catalyzed reaction proceeds via initial generation of the [Zn{RC(=O)NHNH₂}₃](ZnCl₄) complexes (exemplified by isolation of the complex with R = Ph, 76%; characterized by HRESI⁺-MS, IR, CP-MAS TOSS ¹³C{¹H} NMR, and XRD). Electronic effects of substituents at the acyl hydrazide moiety do not significantly affect the reaction rate and the yield of the target triazoles, whereas the steric hindrances reduce the reaction rate without affecting the yield of the heterocycles.

Theoretical insight into the zinc(ii)-catalyzed synthesis of 2-indolyltetrahydroquinolines from N-propargylanilines and indoles: cross-dehydrogenative coupling with temporally separated catalytic activity

An abnormal catalytic cascade reaction with temporally separated catalytic activity.

Expedient stereospecific Co-catalyzed tandem C–N and C–O bond formation of N-methylanilines with styrene oxides

The Co(ii)-catalyzed stereospecific sequential C–N and C–O bond formation of styrene oxides with N-methylanilines has been developed. Optically active epoxides can be coupled with high enantiomeric purity.