Expeditious Synthesis of Multisubstituted Quinolinone Derivatives Based on Ring Recombination Strategy

Stereoselective synthesis of 6/7/6-fused heterocycles with multiple stereocenters via an internal redox reaction/inverse electron-demand hetero-Diels-Alder reaction sequence

A highly stereoselective synthesis of fused heterocycles with multiple stereocenters via an internal redox reaction/inverse electron-demand hetero-Diels-Alder (IEDHDA) reaction sequence is described. The present reaction sequence has three interesting features: (1) complete control of two potentially competitive processes, i.e., hetero-Diels-Alder reaction and [1,5]-hydride shift; (2) one-shot construction of the complicated 6/7/6-fused heterocyclic structure having multiple stereocenters; and (3) high control of its stereoselectivity. When alkenylidene barbiturates with an allyl benzyl ether moiety were treated with a catalytic amount of Sc(OTf)3 and 2,2'-bipyridine, the internal redox reaction/IEDHDA reaction proceeded successively to afford 6/7/6-fused heterocycles in good chemical yields with good to excellent diastereoselectivities.

Intramolecular Palladium(II)-Catalyzed Regioselective 6-endo or 6-exo C-H Benzannulation: An Approach for the Diversity-Oriented Synthesis of Quinolinone Derivatives from Pyridones

Herein, a new intramolecular palladium(II)-catalyzed regioselective 6-endo-trig or 6-exo-trig annulation through direct C-H activation is presented as a method for the diversity-oriented synthesis of highly substituted quinolinones from pyridones. The reaction occurs under mild conditions and exhibits excellent regioselectivity, good functional group tolerance, and broad applications. This innovative approach has been successfully utilized in the synthesis of Glycopentanolone A and an intermediate of (R)-(+)-Tipifarnib.

Divergent synthesis of multi-substituted phenanthrenes via an internal redox reaction/ring expansion sequence

We report an effective synthetic route to multi-substituted phenanthrenes via an internal redox reaction/ring expansion sequence. The interesting feature of the present system is that it allows for the divergent synthesis of the target skeleton depending on the selected Lewis acid catalyst. When benzylidene malonates with a cyclic structure at the ortho-position were treated with BF3·OEt2, three sequential processes (internal redox reaction/elimination of the alkoxy group/ring expansion) proceeded to give phenanthrene derivatives in which the alkoxycarbonyl (CO2R) group and the alkyl (R) group were in close proximity to each other, in good chemical yields. In sharp contrast, treatment with Bi(OTf)3 exclusively led to the formation of another type of phenanthrene, whose R group was positioned distal to the CO2R group.

Novel Multi-Target Agents Based on the Privileged Structure of 4-Hydroxy-2-quinolinone

In this work, the privileged scaffold of 4-hydroxy-2quinolinone is investigated through the synthesis of carboxamides and hybrid derivatives, as well as through their bioactivity evaluation, focusing on the ability of the molecules to inhibit the soybean LOX, as an indication of their anti-inflammatory activity. Twenty-one quinolinone carboxamides, seven novel hybrid compounds consisting of the quinolinone moiety and selected cinnamic or benzoic acid derivatives, as well as three reverse amides are synthesized and classified as multi-target agents according to their LOX inhibitory and antioxidant activity. Among all the synthesized analogues, quinolinone-carboxamide compounds 3h and 3s, which are introduced for the first time in the literature, exhibited the best LOX inhibitory activity (IC50 = 10 μM). Furthermore, carboxamide 3g and quinolinone hybrid with acetylated ferulic acid 11e emerged as multi-target agents, revealing combined antioxidant and LOX inhibitory activity (3g: IC50 = 27.5 μM for LOX inhibition, 100% inhibition of lipid peroxidation, 67.7% ability to scavenge hydroxyl radicals and 72.4% in the ABTS radical cation decolorization assay; 11e: IC50 = 52 μM for LOX inhibition and 97% inhibition of lipid peroxidation). The in silico docking results revealed that the synthetic carboxamide analogues 3h and 3s and NDGA (the reference compound) bind at the same alternative binding site in a similar binding mode.

Lewis acid-catalyzed formal 1,3-aminomethyl migration

Here we report a Lewis acid-catalyzed 1,3-aminomethyl migration rection. When δ-amino acid derivatives were treated with a catalytic amount of Sc(OTf)3, 1,3-migration of the aminomethyl group proceeded smoothly to afford β-amino acid derivatives in moderate to good chemical yields. Detailed investigation suggested that this migration reaction proceeded through the fragmentation/recombination pathway.

[1,5]-Hydride Shift Triggered N-Dealkylative Cyclization into 2-Oxo-1,2,3,4-tetrahydroquinoline-3-carboxylates via Boronate Complexes

A new simple one-pot two-step protocol for the synthesis of 2-oxo-1,2,3,4-tetrahydroquinoline-3-carboxylate from 2-(2-(benzylamino)benzylidene)malonate under the action of BF3·Et2O was developed. It was shown that the reaction proceeds through the formation of a stable iminium intermediate containing a difluoroboryl bridge in the dicarbonyl fragment of the molecule.

peri-Interactions in 1,8-bis(dimethylamino)naphthalene ortho-ketimine cations facilitate [1,5]-hydride shift: selective synthesis of 1,2,3,4-tetrahydrobenzo[h]quinazolines

Selective heterocyclization leading to 1,2,3,4-tetrahydrobenzo[h]quinazolines from ortho-ketimines of 1,8-bis(dimethylamino)naphthalene (DmanIms) under acid catalysis has been revealed. In contrast to the rather unreactive N,N-dimethylaniline ortho-ketimine, DmanIms readily undergo this transformation without an additional catalyst. This distinction in the reactivity underscores the importance of the second peri-NMe₂ group in DmanIms, which facilitates a [1,5]-hydride shift and the subsequent cyclization. The cascade of peri-interactions emerging between 1-NMe₂ and 8-NMe₂ groups has been identified as a reason for the catalytic effect: (1) the hydrogen bond in the DmanIm dication constrains 1-NMe₂ in the desired position providing proximity of reaction centers, (2) the repulsion of the lone pairs of 8-NMe₂ group and unrelaxed 1-NMe₂ group arising right after deprotonation process reduces the Gibbs free energy of activation (ΔG^‡) for the straight hydride shift, and (3) the electrostatic interaction between 8-NMe₂ and the charged NCH₂⁺ group in the intermediate increases the ΔG^‡ for the reverse hydride shift.

15.4.5 Quinolinones and Related Systems (Update 2022)

Quinolinones, of which the quinolin-4(1H)-one ring system can be highlighted, represent an exciting class of nitrogen heterocycles. The quinolinone motif can be found in many natural compounds and approved drugs for several diseases. This chapter is a comprehensive survey of the methods for the synthesis of quinolin-2(1H)-ones, quinolin-4(1H)-ones, and their thio- and amino derivatives, and is an update to the previous Science of Synthesis chapter (Section 15.4), covering the period between 2003 and 2020.

Redox-triggered dearomative [5 + 1] annulation of indoles with O-alkyl ortho-oxybenzaldehydes for the synthesis of spirochromanes

The dearomative [5 + 1] annulation of 2-methylindoles with new five-membered synthon was developed through cascade [1,5]-hydride transfer/dearomative cyclization in HFIP for the synthesis of spirochromanes bearing the 2-methylindolenine skeleton.

HFIP-mediated three-component imidization of electron-rich arenes with in situ formed spiroindolenines for facile construction of 2-arylspiroindolenines

The three-component reaction of o-aminobenzaldehydes with 5-hydroxyindole and electron-rich arenes has been achieved through HFIP-mediated cascade hydride transfer/dearomative cyclization/CDC-type imidization at room temperature under air.

Borane-catalyzed cascade Friedel–Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization to afford tetrahydroquinolines

We report a redox-neutral annulation reaction of tertiary amines with electron-deficient alkynes under metal-free and oxidant-free conditions.

Diastereoselective Synthesis of Dihydro-quinolin-4-ones by a Borane-Catalyzed Redox-Neutral endo-1,7-Hydride Shift

The borane-catalyzed synthesis of dihydroquinoline-4-ones is developed. The amino-substituted chalcones undergo a 1,7-hydride shift upon Lewis acid activation to form a zwitterionic iminium enolate, which collapses to the dihydroquinoline-4-one scaffold. The reaction proceeds in high yields (75-99%) with an excellent diastereoselectivity of up to >99:1 (cis:trans). The reaction mechanism is investigated by kinetic, isotope labeling, and computational experiments.

Ring expansion and ring opening of 3-halooxindoles with N-alkoxycarbonyl-O-tosylhydroxylamines for divergent access to 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas

The reaction of N-alkoxycarbonyl-O-tosylhydroxylamines with indol-2-ones in situ generated from 3-halooxindoles has been developed for divergently accessing 4-aminoquinolin-2-ones and N-Cbz-N’-arylureas in good to excellent yields.

Rapid access to 3-indolyl-1-trifluoromethyl-isobenzofurans by hybrid use of Lewis/Brønsted acid catalysts

We report herein a rapid access to 3-indolyl-1-trifluoromethyl-isobenzofurans via a [1,4]-hydride shift/cyclizatin/intermolecular nucleophilic addition reaction sequence. In this process, a Lewis acid promoted internal redox reaction ([1,4]-hydride shift/cyclization) followed by a Brønsted acid promoted intermolecular reaction (generation of cyclic oxonium cation/intermolecular Friedel-Crafts reaction) occurred to give various 3-indolyl-1-trifluoromethyl-isobenzofurans in good chemical yields.

Hydride Transfer Initiated Redox-Neutral Cascade Cyclizations of Aurones: Facile Access to [6,5] Spirocycles

Reported herein is the hydride transfer initiated redox-neutral cascade cyclizations of aurones, providing a variety of [6,5] spiro-heterocycles in satisfactory yields and good diastereoselectivities.

Hydride transfer enabled switchable dearomatization of indoles in the carbocyclic ring and the pyrrole ring

Hydride transfer enabled the first success of the regioselective dearomatization of indoles in the carbocyclic ring and the pyrrole ring, which was induced by ortho-quinone methides and vinylogous iminium intermediates, respectively.